Infrared-light-transmitting ink of dark color, and infrared-light-reflecting sheet obtained using same

ABSTRACT

In order to satisfy the demand of consumers regarding design attractiveness, an infrared-light-transmitting dark color ink is provided, the ink having a black appearance and attaining high design attractiveness and, despite this, having sufficient infrared-light-transmitting property. The infrared-light-transmitting dark color ink transmits near infrared light having wavelengths of 750-1,500 nm, and comprises a resin component and a pigment component that comprises both a brown pigment, e.g., a benzimidazolone pigment, and a phthalocyanine pigment.

TECHNICAL FIELD

The present invention relates to an infrared-light-transmitting darkcolor ink. More specifically, the present invention relates to aninfrared-light-transmitting dark color ink mainly used in aninfrared-light-reflecting sheet for a solar cell module, or the like.

BACKGROUND ART

In recent years, solar cells have been receiving attention as a cleanenergy source due to the rise in awareness of environmental problems. Ingeneral, a solar cell module constituting a solar cell has aconfiguration in which a transparent front substrate, a sealingmaterial, a solar cell element, a sealing material, and a rear surfaceprotective sheet are laminated sequentially from the photoreceptionsurface side, and has a function of generating electric power bysunlight being incident on the solar cell element.

For example, regarding inks used in solar cell modules and the like,from the viewpoint of design attractiveness, inks the appearance ofwhich is colored with black are required in some cases. As a method ofcoloring appearance with a dark color, a method of providing an inkcontaining carbon black is mentioned. However, carbon black absorbs nearinfrared light to cause an increase in temperature, and thus it cannotbe said that, when the ink containing carbon black is used, for example,in solar cell modules and the like, the ink containing carbon black isnecessarily preferable.

When the ink containing carbon black is used in a rear surfaceprotective sheet for a solar cell module, the temperature of the solarcell module is increased at the time of using the solar cell module. Asa result, the electric power generation efficiency of the solar cellmodule is decreased.

In this regard, a rear surface protective sheet for a solar cell modulehas been developed which includes a black resin layer containing anorganic pigment such as an oxazine pigment having aninfrared-light-transmitting property, a white resin layer havinginfrared reflectivity, a rear surface protective layer having weatherresistance, and the like in order to suppress heat generation in a darkcolor layer and to cause reflective light to be incident to a solar cellelement so that electric power generation efficiency is improved andwhich is produced by attaching this plurality of layers to each otherwith an adhesive or the like.

(Patent Document 1).

An infrared-light-transmitting dark color ink containing an oxazinepigment and a curing agent becomes an infrared-light-transmitting darkcolor ink having high durability of adhesion. (Patent Document 1[0057]). However, the oxazine pigment transmits light having awavelength of 700 to 800 nm, and thus the oxazine pigment itself is apigment having a color close to violet rather than black. For thisreason, the infrared-light-transmitting dark color ink in which theoxazine pigment is included in a resin has a color close to violet.Therefore, it cannot be said that the infrared-light-transmitting darkcolor ink in which the oxazine pigment is included in a resin isnecessarily preferable when a black appearance is required from theviewpoint of design attractiveness.

In particular, when the infrared-light-transmitting dark color ink isused in the rear surface protective sheet of the solar cell module, thedemand for the electric power generation efficiency of the solar cellmodule becomes even stronger. The infrared-light-transmitting dark colorink used in the rear surface protective sheet is required to be aninfrared-light-transmitting dark color ink which further transmitsinfrared light. The infrared-light-transmitting dark color ink whichtransmits infrared light can suppress increases in temperature of thesolar cell module by suppressing absorption of near infrared light. Inaddition, by utilizing infrared light in electric power generation, theelectric power generation efficiency of the solar cell module can befurther enhanced. Therefore, it is important to use theinfrared-light-transmitting dark color ink which further transmitsinfrared light.

Patent. Document 1: Japanese Unexamined Patent Application, Publication.No, 2012-216689

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

An object of the present invention is to provide an excellentinfrared-light-transmitting dark color ink which is an ink capable ofproviding a dark color appearance to a rear surface protective sheet fora solar cell module and has a high near infrared transmission rate.

Means for Solving the Problems

The present inventors have conducted intensive studies in order to solvethe above-described problems. As a result, they have found that theabove-described problems can be solved with aninfrared-light-transmitting dark color ink which contains a pigmentcomponent containing a predetermined brown pigment and a phthalocyaninepigment, and thus have completed the present invention. Morespecifically, the present invention provides the following.

(1) An infrared-light-transmitting dark color ink which transmits nearinfrared light having a wavelength of 750 nm to 1500 nm, theinfrared-light-transmitting dark color ink containing: a resin componentand a pigment component, in which the pigment component contains a brownpigment and a dark color pigment composed of a phthalocyanine pigment,and the brown pigment is at least one or more pigments selected from thegroup consisting of a benzimidazolone pigment,4-[(2,5-dichlorophenyl)azo]-3-hydroxy-N-(2,5-dimethoxyphenyl)-2-naphthalenecarboxamide,1-[(4-nitrophenyl)azo]-2-naphthalenol,bis[3-hydroxy-4-(phenylazo)-2-naphthalenecarboxylic acid]copper salt, C.I. Pigment Brown 7,N,N′-bis(2,4-dinitrophenyl)-3,3′-dimethoxy-1,1′-biphenyl-4,4′-diamine,3,4,9,10-perylenetetracarboxylic diimide,Δ2,2′(1H,1′H)-binaphtho[2,1-b]thiophen-1,1′-dione, andN,N′-(10,15,16,17-tetrahydro-5,10,15,17-tetraoxo)-5H-dinaphtho[2,3-a:2′,3′-i]carbazole-4,9-diyl)bis(benzamide).

(2) The infrared-light-transmitting dark color ink described in (1), inwhich a content of the dark color pigment in the pigment component is80% by mass or more, and

a transmission rate of light having a wavelength of 425 nm of theinfrared-light-transmitting dark color ink in a light transmission ratetest is 5% to 30%, and a transmission rate of light having a wavelengthof 675 nm is 4% to 20%.

(3) The infrared-light-transmitting dark color ink described in (1) or(2), in which a content of the pigment component is 20 parts by mass to40 parts by mass with respect to 100 parts by mass of the resincomponent.

(4) An infrared-light-reflecting sheet including aninfrared-light-transmitting dark color layer laminated on a surface of areflective layer reflecting near infrared light having a wavelength of750 nm to 1500 nm, in which the infrared-light-transmitting dark colorlayer contains a main agent resin having a hydroxyl group, a curingagent having an isocyanate group, and a pigment component, the pigmentcomponent contains a brown pigment and a dark color pigment composed ofa phthalocyanine pigment, and the brown pigment is at least one or morepigments selected from the group consisting of a benzimidazolonepigment,4-[(2,5-dichlorophenyl)azo]-3-hydroxy-N-(2,5-dimethoxyphenyl)-2-naphthalenecarboxamide,1-[(4-nitrophenyl)azo]-2-naphthalenol,bis[3-hydroxy-4-(phenylazo)-2-naphthalenecarboxylic acid]copper salt, C.I. Pigment Brown 7,N,N′-bis(2,4-dinitrophenyl)-3,3′-dimethoxy-1,1′-biphenyl-4,4′-diamine,3,4,9,10-perylenetetracarboxylic diimide,Δ2,2′(1H,1′H)-binaphtho[2,1-b]thiophen-1,1′-dione, andN,N′-(10,15,16,17-tetrahydro-5,10,15,17-tetraoxo)-5H-dinaphtho[2,3-a:2′,3′-i]carbazole-4,9-diyl)bis(benzamide).

(5) The infrared-light-reflecting sheet described in (4), furtherincluding a transparent easy-adhesive layer laminated on the surface onthe lamination side of the infrared-light-transmitting dark color layerof the infrared-light-reflecting sheet.

(6) An infrared-light-reflecting sheet including aninfrared-light-transmitting dark color layer and a transparent resinlayer sequentially laminated on a surface of a reflective layerreflecting near infrared light having a wavelength of 750 nm to 1500 nm,in which the infrared-light-transmitting dark color layer contains amain agent resin having a hydroxyl group, a curing agent having anisocyanate group, and a pigment component, a content of the pigmentcomponent is 20 parts by mass to 40 parts by mass with respect to 100parts by mass of a resin component, the pigment component contains abrown pigment and a dark color pigment composed of a phthalocyaninepigment, and the brown pigment is at least one or more pigments selectedfrom the group consisting of a benzimidazolone pigment,4-[(2,5-dichlorophenyl)azo]-3-hydroxy-N-(2,5-dimethoxyphenyl)-2-naphthalenecarboxamide,1-[(4-nitrophenyl)azo]-2-naphthalenol,bis[3-hydroxy-4-(phenylazo)-2-naphthalenecarboxylic acid]copper salt, C.I. Pigment Brown 7,N,N′-bis(2,4-dinitrophenyl)-3,3′-dimethoxy-1,1′-biphenyl-4,4′-diamine,3,4,9,10-perylenetetracarboxylic diimide,Δ2,2′(1H,1′H)-binaphtho[2,1-b]thiophen-1,1′-dione, andN,N′-(10,15,16,17-tetrahydro-5,10,15,17-tetraoxo)-5H-dinaphtho[2,3-a:2′,3′-i]carbazole-4,9-diyl)bis(benzamide).

(7) The infrared-light-reflecting sheet described in (6), in which acoating amount of an infrared-light-transmitting dark color ink formingthe infrared-light-transmitting dark color layer in terms of solidcontent is 5 g/m² to 15 g/m².

(8) The infrared-light-reflecting sheet described in any one of (4) to(7), in which a color difference ΔE*ab between a color tone of theinfrared-light-transmitting dark color layer 60 and a color tone ofcarbon black as measured under conditions of a D65 light source and a10° view angle according to JIS-Z 8722 is 10 or less.

(9) An infrared-light-reflecting sheet which is a rear surfaceprotective sheet for a solar cell module, the infrared-light-reflectingsheet being obtained by laminating a plurality of layers, the pluralityof layers including at least: a transparent adhesion layer transmittingall light beams; and a reflective layer reflecting near infrared lighthaving a wavelength of 750 nm to 1500 nm, in which two layers amonglayers laminated between the transparent adhesion layer and thereflective layer are an infrared-light-transmitting dark color layer anda transparent adhesive layer, the infrared-light-transmitting dark colorlayer contains a main agent resin having a hydroxyl group, a curingagent, having an isocyanate group, and a pigment component, a content ofthe pigment component contained in the infrared-light-transmitting darkcolor layer is 20 parts by mass to 50 parts by mass with respect to 100parts by mass of the main agent resin, the pigment component contains abrown pigment and a dark color pigment composed of a phthalocyaninepigment, the brown pigment is at least one or more pigments selectedfrom the group consisting of a benzimidazolone pigment,4-[(2,5-dichlorophenyl)azo]-3-hydroxy-N-(2,5-dimethoxyphenyl)-2-naphthalenecarboxamide,1-[(4-nitrophenyl)azo]-2-naphthalenol,bis[3-hydroxy-4-(phenylazo)-2-naphthalenecarboxylic acid]copper salt, C.I. Pigment Brown 7,N,N′-bis(2,4-dinitrophenyl)-3,3′-dimethoxy-1,1′-biphenyl-4,4′-diamine,3,4,9,10-perylenetetracarboxylic diimide,Δ2,2′(1H,1′H)-binaphtho[2,1-b]thiophen-1,1′-dione, andN,N′-(10,15,16,17-tetrahydro-5,10,15,17-tetraoxo)-5H-dinaphtho[2,3-a:2′,3′-i]carbazole-4,9-diyl)bis(benzamide),and an NCO/OH ratio that is a ratio of an NCO value of the curing agentto an OH value of the main agent resin is 1.0 to 2.0.

(10) The infrared-light-reflecting sheet described in (9), in which acoating amount of an infrared-light-transmitting dark color ink formingthe infrared-light-transmitting dark color layer in terms of solidcontent is 3 g/m² to 7 g/m².

(11) The infrared-light-reflecting sheet described in (9) or (10), inwhich the curing agent having an isocyanate group is a diisocyanatecompound.

(12) The infrared-light-reflecting sheet described in any one of (9) to(11), in which the infrared-light-transmitting dark color layer islaminated only on a part of the surface of the transparent adhesionlayer and/or the reflective layer.

(13) The infrared-light-reflecting sheet described in any one of (4) to(12), in which an infrared-light-transmitting coat layer containing anorganic dark color pigment is laminated on a surface opposite to thelamination surface of the infrared-light-transmitting dark color layerof the reflective layer, and the infrared.-light-transmitting coat layertransmits near infrared light having a wavelength of 750 nm to 1500 nm.

(14) A solar cell module including the infrared-light-reflecting sheetdescribed in any one of (4) to (13) laminated on a non-photoreceptionsurface side of a solar cell element.

EFFECTS OF THE INVENTION

The infrared-light-transmitting dark color ink of the present inventioncan suppress heat generation caused by absorption of near infrared lighteven in an environment in which sunlight is radiated. Theinfrared-light-reflecting sheet of the present invention obtained byusing the infrared-light-transmitting dark color ink in theinfrared-light-reflecting sheet (rear surface protective sheet) for asolar cell module sufficiently satisfies design attractiveness. Further,when the infrared-light-reflecting sheet suppresses heat generationcaused by absorption of near infrared light and is used as the rearsurface protective sheet for the solar cell module, theinfrared-light-reflecting sheet can also contribute to an increase inthe electric power generation efficiency of the solar cell module.Therefore, when the infrared-light-transmitting dark color ink of thepresent invention is used as the rear surface protective sheet for thesolar cell module, this rear surface protective sheet is an excellentrear surface protective sheet.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional schematic view illustrating an example of a layerstructure of a solar cell module.

FIG. 2 is a diagram provided to describe a layer structure of aninfrared-light-reflecting sheet and is an enlarged sectional schematicview in a state where the infrared-light-reflecting sheet is integratedwith the solar cell module when the infrared-light-reflecting sheet isused as a rear surface protective sheet for the solar cell module.

FIG. 3 is a graph showing infrared reflection rates of Example 1 andComparative Example 1.

FIG. 4 is a diagram illustrating color coordinates of Examples 2 to 4.

FIG. 5 is a diagram illustrating color coordinates of ComparativeExamples 2 to 6.

FIG. 6 is a diagram provided to describe a layer structure of aninfrared-light-reflecting sheet of another embodiment and is an enlargedsectional schematic view in a state where the infrared-light-reflectingsheet is integrated with the solar cell module when theinfrared-light-reflecting sheet is used as a rear surface protectivesheet for the solar cell module.

FIG. 7 is a diagram illustrating color coordinates of Examples 13 to 15.

PREFERRED MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an infrared-light-transmitting dark color ink of thepresent invention will be described in detail. The present invention isnot limited to the embodiments described below.

<Infrared-Light-Transmitting Dark Color Ink>

An infrared-light-transmitting dark color ink of the present inventioncan be used for coloring an rear surface protective sheet for a solarcell module, or the like with a dark color from the viewpoint of designattractiveness. The infrared-light-transmitting dark color ink has ahigh near infrared light transmission rate. For this reason, heatgeneration caused by the absorption of near infrared light can besuppressed. For example, when an infrared-light-transmitting dark colorlayer 60 is formed by the infrared-light-transmitting dark color ink ofthe present invention on a surface of a reflective sheet which canreflect near infrared light, an infrared-light-reflecting sheet whichcan reflect near infrared light while the appearance thereof is darklycolored can be produced.

When the infrared-light-transmitting dark color ink of the presentinvention contains a curing agent, the infrared-light-transmitting darkcolor ink becomes an infrared-light-transmitting dark color ink capableof attaching sheets to each other. For example, theinfrared-light-transmitting dark color layer can be formed by applyingthe infrared-light-transmitting dark color ink containing a curing agentonto a sheet, laminating another sheet thereto, and by curing theinfrared-light-transmitting dark color ink.

An infrared-light-reflecting sheet 6 may be formed by sequentiallylaminating the infrared-light-transmitting dark color layer 60 and atransparent adhesion layer 62 on a surface of a reflective layer 61reflecting near infrared light. For example, theinfrared-light-reflecting sheet 6 of the present invention can also beused as a rear surface protective sheet for a solar cell module bydisposing the infrared-light-reflecting sheet 6 on a non-photoreceptionsurface side of the solar cell element.

From the viewpoint of design attractiveness, there is a case where theentire surface of the infrared-light-reflecting sheet 6 is not darklycolored, but a partially colored infrared-light-reflecting sheet 6 isrequired, for example, for providing a design such as patterning. Whenthe infrared-light-reflecting sheet 6 of the embodiment of FIG. 6 isused as the rear surface protective sheet for the solar cell module, therear surface protective sheet becomes an excellent rear surfaceprotective sheet for a solar cell module which is excellent in designattractiveness and can maintain electric power generation efficiency ashigh as that of the related art. The infrared-light-reflecting sheet 6of the embodiment of FIG. 6 will be described later.

As illustrated in FIG. 2 or 6, the infrared-light-reflecting sheet canbe formed by curing the infrared-light-transmitting dark color ink,which is applied to the upper surface of the reflective layer 61 or thelower surface of the transparent adhesion layer 62 facing the uppersurface, after lamination. When the infrared-light-transmitting darkcolor layer 60 is formed at a position between the reflective layer 61and the transparent adhesion layer 62, the infrared-light-reflectingsheet 6 can be configured as a favorable sheet in terms of designattractiveness.

It is important for the infrared-light-transmitting dark color inkforming the infrared-light-transmitting dark color layer 60 that theappearance thereof is black or has a dark color close to black, that is,the infrared-light-transmitting dark color ink has properties ofabsorbing visible light and transmitting near infrared light.

Herein, near infrared light is a range nearest a visible range amonginfrared ranges, but regarding specific wavelength ranges of nearinfrared light, values thereof are various depending on the literature.The near infrared light described in the present invention indicates anelectromagnetic wave having a wavelength range of 750 nm to 2200 nm.Among them, particularly, a wavelength promoting heat accumulation is1000 nm to 1500 nm.

For the infrared-light-transmitting dark color ink forming theinfrared-light-transmitting dark color layer 60, aninfrared-light-transmitting dark color ink having a property oftransmitting a light beam having a wavelength of 750 nm to 1500 nm in acured state is used. Incidentally, the expression “transmitting a lightbeam having a wavelength of 750 nm to 1500 nm” means transmitting 15% ormore of the light beam having a wavelength of 750 nm to 1500 nm in theinfrared-light-transmitting dark color layer 60, preferably meanstransmitting 50% or more of the light beam, and more preferably meanstransmitting 60% or more of the light beam.

The infrared-light-transmitting dark color ink used in theinfrared-light-transmitting dark color layer 60 can be used forattaching sheets to each other. When the infrared-light-transmittingdark color ink is used in this way, the infrared-light-transmitting darkcolor ink is preferably a two-component type including a main agent anda curing agent. From the viewpoint of coating property and handlingproperty, a solvent is suitably contained as a composition.

[Organic Pigment]

A pigment component contained in the infrared-light-transmitting darkcolor ink of the present invention contains a dark color pigmentcomposed of a brown pigment and a phthalocyanine pigment. The brownpigment will be hereinafter described in detail. Theinfrared-light-transmitting dark color ink of the present inventionwhich contains a pigment component containing such a dark color pigmentis an excellent ink that has dark color appearance and a high infraredlight transmission rate.

In the present specification, the brown pigment is at least one or morepigments selected from the group consisting of a benzimidazolonepigment,4-[(2,5-dichlorophenyl)azo]-3-hydroxy-N-(2,5-dimethoxyphenyl)-2-naphthalenecarboxamide,1-[(4-nitrophenyl)azo]-2-naphthalenol,bis[3-hydroxy-4-(phenylazo)-2-naphthalenecarboxylic acid]copper salt,N,N′-bis(2,4-dinitrophenyl)-3,3′-dimethoxy-1,1′-biphenyl-4,4′-diamine,3,4,9,10-perylenetetracarboxylic diimide,Δ2,2′(1H,1′H)-binaphtho[2,1-b]thiophen-1,1′-dione, andN,N′-(10,15,16,17-tetrahydro-5,10,15,17-tetraoxo-5H-dinaphtho[2,3-a:2′,3′-i]carbazole-4,9-diyl)bis(benzamide).

The brown pigment is preferably a benzimidazolone pigment from theviewpoint of dispersibility of the pigment in the adhesive layer andadhesiveness of the adhesive layer, and the like. The benzimidazolonepigment is a pigment having a benzimidazolone skeleton represented bythe following General Formula (1). Specific examples thereof include C.I. Pigment Yellow 120, C. I. Pigment Yellow 151, C. I. Pigment Yellow154, C. I. Pigment Yellow 175, C. I. Pigment Yellow 180, C. I. PigmentYellow 181, C. I. Pigment Yellow 194, C. I. Pigment Red 175, C. I.Pigment Red 176, C. I. Pigment Red 185, C. I. Pigment Red 208, C. I.Pigment Violet 32, C. I. Pigment Orange 36, C. I. Pigment Orange 62, C.I. Pigment Orange 72, and C. I. Pigment Brown 25, but thebenzimidazolone pigment is not limited thereto. From the viewpoint ofcolor gamut, C. I. Pigment Brown 25 is more preferable.

The primary particle diameter of the benzimidazolone pigment ispreferably 0.01 μm to 0.20 μm. When the primary particle diameter of thebenzimidazolone pigment is set in such a range, dispersibility of thepigment in the ink can be improved.

Brown pigments other than the benzimidazolone pigment will be described.Specific examples of4-[(2,5-dichlorophenyl)azo]-3-hydroxy-N-(2,5-dimethoxyphenyl)-2-naphthalenecarboxamideinclude C. I. Pigment Brown 1. Specific examples of1-[(4-nitrophenyl)azo]-2-naphthalenol include C. I. Pigment Brown 2.Specific examples of bis[3-hydroxy-4-(phenylazo)-2-naphthalenecarboxylicacid]copper salt include C. I. Pigment Brown 5. Specific examples ofN,N′-bis(2,4-dinitrophenyl)-3,3′-dimethoxy-1,1′-biphenyl-4,4′-diamineinclude C. I. Pigment Brown 22. Specific examples of3,4,9,10-perylenetetracarboxylic diimide include C. I. Pigment Brown.26. Specific examples ofΔ2,2′(1H,1′H)-binaphtho[2,1-b]thiophen-1,1′-dione include C. I. PigmentBrown 27. Specific examples ofN,N′-(10,15,16,17-tetrahydro-5,10,15,17-tetraoxo-5H-dinaphtho[2,3-a:2′,3′-i]carbazole-4,9-diyl)bis(benzamide)include C. I. Pigment Brown 28. In addition to the above-described brownpigments, C. I. Pigment Brown 7 may be used as the brown pigment.

The phthalocyanine pigment is a pigment having a phthalocyanine skeletonand is a concept including phthalocyanine in which various metals arecoordinated. Specific examples thereof include C. I. Pigment Green 7, C.I. Pigment Green 36, C. I. Pigment Green 37, C. I. Pigment Blue 16, C.I. Pigment Blue 75, and C. I. Pigment Blue 15, but the phthalocyaninepigment is not limited thereto. A phthalocyanine pigment that isamorphous and blue is preferably used.

The primary particle diameter of the phthalocyanine pigment ispreferably 0.15 μm to 0.20 μm. When the primary particle diameter is setin such a range, dispersibility of the phthalocyanine pigment in the inkcan be improved.

The content of the brown pigment in the infrared-light-transmitting darkcolor ink is preferably set to 43 parts by mass to 233 parts by masswith respect to 100 parts by mass of the phthalocyanine pigment (thecontent ratio of the brown pigment and the phthalocyanine pigment is ina range of 30:70 to 70:30 in terms of mass ratio), and more preferably66 parts by mass to 150 parts by mass (the content ratio of the brownpigment and the phthalocyanine pigment is in a range of 40:60 to 60:40in terms of mass ratio). When the content ratio is in such a range, theinfrared-light-transmitting dark color ink can be configured as afavorable ink in terms of design attractiveness andinfrared-light-transmitting property.

The content of the brown pigment in the infrared-light-transmitting darkcolor ink can be specified by a transmission rate of light having aspecific wavelength in the light transmission rate test. In order toadjust the content of the brown pigment such as a benzimidazolonepigment and the content of the phthalocyanine pigment to be preferablein terms of design attractiveness and infrared-light-transmittingproperty, it is preferable that the brown pigment such as abenzimidazolone pigment and the phthalocyanine pigment contained in theinfrared-light-transmitting dark color ink are 80% by mass or more ofthe total amount of the pigment component, a transmission rate of lighthaving a wavelength of 425 nm of the infrared-light-transmitting darkcolor ink in the light transmission rate test is 5% to 30%, and atransmission rate of light having a wavelength of 675 nm is 4% to 20%.The phthalocyanine pigment has properties of transmitting a certainquantity of light having a wavelength of 425 nm and not transmittinglight having a wavelength of 675 nm. The brown pigment such as abenzimidazolone pigment has properties of transmitting a certainquantity of light having a wavelength of 675 nm and not transmittinglight having a wavelength of 425 nm. Therefore, by specifying thetransmission rate of light having a wavelength of 425 nm and thetransmission rate of light having a wavelength of 675 nm in the lighttransmission rate test, the content ratio of the content of the brownpigment such as a benzimidazolone pigment and the content or thephthalocyanine pigment can be specified.

Incidentally, as a method for measuring the transmission rate of theinfrared-light-transmitting dark color ink, the transmission rate can bemeasured, for example, with the following method.

5 g/m² of the infrared-light-transmitting dark color ink containing acuring agent is gravure coated on white PET (188 μm), polyethylene (60μm) is laminated thereon, and the obtained product is subjected tothermal curing by performing an aging treatment at 45° C. to 55° C. for168 hours, thereby producing an infrared-light-reflecting sheet. Then, atransmission rate measurement sample of a solution obtained by peelingoff polyethylene and the white PET of the infrared-light-reflectingsheet and dissolving the infrared-light-transmitting dark color layer(infrared-light-transmitting dark color ink) by using methyl ethylketone is produced (for example, the pigment concentration of themeasurement sample is about 0.01 g to 0.5 g of the pigment with respectto 100 g of methyl ethyl ketone). The content of the brown pigment inthe infrared-light-transmitting dark color ink can be estimated byinjecting the measurement sample into a quartz glass cell, measuring atransmission rate (%) of light having a wavelength of 300 nm to 1200 nmwith a spectrophotometer (for example, an ultraviolet spectrophotometer“V-670” manufactured by JASCO Corporation or “U-4100” manufactured byHitachi High-Technologies Corporation), and then obtaining atransmission rate of light having a wavelength of 425 nm and of lighthaving a wavelength of 675 nm.

As a method for measuring the transmission rate of theinfrared-light-transmitting dark color layer formed by theinfrared-light-transmitting dark color ink, the transmission rate can bemeasured with the following method. 5 g/m² of theinfrared-light-transmitting dark color ink containing a curing agent isgravure coated on a fluorine film (100 μm) serving as a transparent basematerial, the same fluorine film (100 μm) is laminated thereon, and theobtained product is subjected to dry lamination and then subjected tothermal curing by performing an aging treatment at 45° C. to 55° C. for168 hours, thereby producing a transmission rate measurement sample.Measurement can be carried out by injecting the measurement sample intoa quartz glass cell, measuring a transmission rate (%) of light having awavelength of 300 nm to 1200 nm with a spectrophotometer (for example,an ultraviolet spectrophotometer “V-670” manufactured by JASCOCorporation or “U-4100” manufactured by Hitachi High-TechnologiesCorporation), and then obtaining a transmission rate of light having awavelength of 425 nm and of light having a wavelength of 675 nm.

The pigment component is contained in the infrared-light-transmittingdark color ink of the present invention. In theinfrared-light-transmitting dark color ink, the content of the pigmentcomponent is preferably 20 parts by mass to 40 parts by mass withrespect to 100 parts by mass of the resin component. Herein, when theinfrared-light-transmitting dark color ink contains a pigment componentcontaining an organic pigment such as an oxazine pigment, it is knownthat when the content of the pigment component is set to 30 parts bymass or more, there is an adverse effect on the adhesiveness of thecuring agent and the adhesiveness of the infrared-light-transmittingdark color layer 60 is decreased. For this reason, it is considered thatthere is difficulty using the infrared-light-transmitting dark color inkparticularly for attaching sheets to each other. However, the brownpigment and the phthalocyanine pigment have higher dispersibility thanother pigments and have a small influence on adhesiveness of the curingagent. Therefore, even when the content ratio of the pigment componentis set to 30 parts by mass or more with respect to 100 parts by mass ofthe resin component, a decrease in adhesiveness and adhesivenessdurability of the infrared-light-transmitting dark color layer 60 can besuppressed to a very small range. As described later, when the blendingratio of the pigment component in the infrared-light-transmitting darkcolor ink is set to be high, the color tone of theinfrared-light-transmitting dark color layer 60 can be stabilized with asmaller coating amount. Incidentally, when the content of the pigmentcomponent in the infrared-light-transmitting dark color ink is set to 40parts by mass or less with respect to 100 parts by mass of the resincomponent, the infrared-light-transmitting dark color layer 60 formed bythe infrared-light-transmitting dark color ink of the present inventioncan be configured as the infrared-light-transmitting dark color layer 60having adhesiveness and adhesion stability.

The infrared-light-transmitting dark color ink of the present inventioncan also contain a curing agent as necessary. According to theinfrared-light-transmitting dark color ink of the present inventioncontaining a curing agent, the infrared-light-transmitting dark colorlayer 60 having favorable adhesion to the resin sheet can be formed. Byadjusting the content of the curing agent contained in theinfrared-light-transmitting dark color ink, theinfrared-light-transmitting dark color layer 60 which can attach sheetsto each other can be formed. Hereinafter, the main agent and the curingagent will be described respectively as an embodiment which canconfigure the resin component contained in theinfrared-light-transmitting dark color ink. Incidentally, the resincomponent related to the present invention is not intended to be limitedto the following embodiment.

[Main Agent Component]

A polyurethane/polycarbonate diol-based component containing a mixtureof polyurethane diol and aliphatic polycarbonate diol can be used as themain agent component of the resin component, for example. Both ofpolyurethane diol and aliphatic polycarbonate diol configuring the mainagent are a polyol having a hydroxyl group and react with a curing agenthaving an isocyanate group to form an adhesive layer. In the presentembodiment, when a mixture obtained by blending a predetermined amountof polyurethane diol and aliphatic polycarbonate diol is used as themain agent, adhesiveness and weather resistance of theinfrared-light-transmitting dark color layer 60 can be improved.

Polyurethane diol which can be used in the main agent component ispolyurethane having a urethane structure as a repeating unit and ahydroxyl group at both terminals thereof. The number average molecularweight of polyurethane diol is preferably 7000 to 13000. When the numberaverage molecular weight is 7000 or more, reactivity with the curingagent is favorable, which is preferable. When the number averagemolecular weight is 13000 or less, dissolving in the solvent isimproved, which is preferable.

The hydroxyl group value of polyurethane diol is preferably in a rangeof 10 mgKOH/g to 50 mgKOH/g. When the hydroxyl group value ofpolyurethane diol is 10 mgKOH/g or more, most of the curing agentcomponent added reacts with a hydroxyl group contained in the main agentcomponent, which is preferable. When the hydroxyl group value is 50mgKOH/g or less, reaction with the curing agent proceeds well, which ispreferable.

Since polyurethane diol improves the adhesiveness and weather resistanceof the main agent component as the main agent component of the adhesive,polyurethane diol is obtained by reacting aliphatic polycarbonate diol,1,6-hexanediol, and isophorone diisocyanate with one another.Hereinafter, aliphatic poly-carbonate diol, 1,6-hexanediol, andisophorone diisocyanate that are constituents of polyurethane diol willbe described.

Aliphatic polycarbonate diol is a constituent of polyurethane diol whichcan react with isophorone diisocyanate described below. Aliphaticpolycarbonate diol has a carbonate structure as a repeating unit and ahydroxyl group at both terminals thereof. The hydroxyl group at bothterminals thereof is capable of curing with an isocyanate group.

Aliphatic polycarbonate diol can be produced with a method for producingaliphatic polycarbonate diol using alkylene carbonate and diol as a rawmaterial or a method for producing aliphatic polycarbonate diol usingdiolkyl carbonate or diaryl carbonate and diol. Aliphatic polycarbonatediol which is used in the present embodiment can be produced byappropriately selecting the production method depending on theperformance necessary for the main agent component.

Examples of alkylene carbonate which can be used for production ofaliphatic polycarbonate diol include ethylene carbonate, trimethylenecarbonate, 1,2-propylene carbonate, 1,2-butylene carbonate, 1,3-butylenecarbonate, and 1,2-pentylene carbonate. Examples of diolkyl carbonateinclude dimethyl carbonate, diethyl carbonate, and dipropyl carbonate,and examples of diaryl carbonate include diphenyl carbonate.

Examples of diol may include a diol having no side chain such asethylene glycol, 1, 3-propanediol, 1, 4-butanediol, 1,5-pentanediol,1,6-hexanediol, or 1,7-heptanediol, a diol having a side chain such as2-methyl-1,8-octanediol, neopentyl glycol, or 2-ethyl-1,6-hexanediol,and a cyclic diol such as 1,3-cyclohexanediol or 1,4-cyclohexanediol.Incidentally, one kind of diol may be used or a copolymer polycarbonatediol having two or more diols as a raw material may be used.

The number average molecular weight of aliphatic polycarbonate diol ispreferably 1000 to 2000. When the number average molecular weight is1000 or more, curing with diisocyanate easily occurs, which ispreferable. When the number average molecular weight is 2000 or less,solubility in the solvent as an adhesive component is improved, which ispreferable in the production of polycarbonate diol, aliphaticpolycarbonate diol has high reactivity as a monomer and is easy tohighly polymerize. For these reason, in order to obtain polycarbonatediol having a predetermined number average molecular weight, it isnecessary to control the reaction speed and the like.

A commercially available product can also be used as the aliphaticpolycarbonate diol. In order to obtain an adhesive that is excellent interms of durability, weather resistance, heat resistance, and hydrolysisresistance, for example, aliphatic polycarbonate diol having a numberaverage molecular weight of 1000 (product name “DURANOL T5651”manufactured by Asahi Kasei Chemicals Corporation) and aliphaticpolycarbonate diol having a number average molecular weight of 2000(product name “DURANOL T5662” manufactured by Asahi Kasei ChemicalsCorporation) can be suitably used.

1,6-hexanediol is an aliphatic diol and can form polyurethane diol byreaction with isophorone diisocyanate described below. 1,6-hexanediol isin a liquid state at normal temperature and can be dissolved in asolvent that is an adhesive component.

Polyester diol can be used together with 1,6-hexanediol. Polyester diolis a polyol having two or more hydroxyl groups, similarly to1,6-hexanediol. Further, polyester diol can form ester with carboxylicacid having a bulky aromatic ring in a basic skeleton thereof. For thisreason, it is possible to provide excellent curing speed and cohesiveforce to polyurethane diol obtained by reaction with isophoronediisocyanate. As polyester diol, for example, aromatic polyester diolproduced by using isophthalic acid can be mentioned. Incidentally,polyester diol in the present embodiment can be produced by selecting acombination of a predetermined carboxylic acid compound and a diolaccording to a standard method.

The number average molecular weight of polyester diol is preferably 3000to 4000. When the number average molecular weight of polyester diol is3000 or more, reactivity with the curing agent is improved, which ispreferable. When the number average molecular weight of polyester diolis 4000 or less, solubility in the solvent is improved, which ispreferable.

Isophorone diisocyanate is a constituent of polyurethane diol and isalicyclic polyisocyanate. Isophorone diisocyanate reacts with a hydroxylgroup of aliphatic polycarbonate diol, 1, 6-hexanediol, or polyesterdiol described above to form polyurethane diol serving as a main agentcomponent.

A solution of polyurethane diol serving as a main agent component can beobtained by dissolving aliphatic polycarbonate diol, aliphatic diol, andisophorone diisocyanate, which are described above, in a solvent, mixingthe resultant solution, and causing the resultant solution to react byheating to reflux. In the reaction, the hydroxyl groups at bothterminals of each of the aliphatic polycarbonate diol and the aliphaticdiol react with an isocyanate group of isophorone diisocyanate to form aurethane bond and then are cured.

The blending ratio of 1, 6-hexanediol in a reaction system in whichpolyurethane diol serving as a main agent component is produced ispreferably 5 parts by mass to 15 parts by mass with respect to 100 partsby mass of aliphatic polycarbonate diol, and more preferably 2 parts bymass to 8 parts by mass. When the blending ratio of 1, 6-hexanediol is 5parts by mass or more, an adhesive component having durability can beobtained, which is preferable. When the blending ratio of 1,6-hexanediol is 15 parts by mass or less, solubility in the solvent isimproved, which is preferable.

The blending ratio of polyester diol in the reaction system in whichpolyurethane diol is produced is preferably 50 parts by mass to 100parts by mass with respect to 100 parts by mass of aliphaticpolycarbonate diol. When the blending ratio of polyester diol is 50parts by mass or more, an adhesive component having durability can beobtained, which is preferable. When the blending ratio of polyester diolis 100 parts by mass or less, solubility in the solvent is improved,which is preferable.

Incidentally, a solvent, which can be used in the case of causingaliphatic polycarbonate diol, aliphatic diol, and isophoronediisocyanate to react with one another, is not particularly limited aslong as it can dissolve these compounds and does not react with thesolvent. For example, from the viewpoint of compatibility with a solventor the like and workability in lamination, a carboxylic acid ester-basedsolvent such as ethyl acetate can be mentioned.

Aliphatic polycarbonate diol serving as a main agent component reactswith a curing agent component having an isocyanate group. The samealiphatic polycarbonate diol which is used when the polyurethane diol isproduced can be used as aliphatic polycarbonate

The main agent component is a mixture of the polyurethane diol and thealiphatic polycarbonate diol described above. Regarding the mass ratioof polyurethane diol and aliphatic polycarbonate diol in the mixture,the content of aliphatic polycarbonate diol is preferably 10 parts bymass to 20 parts by mass with respect to 100 parts by mass ofpolyurethane diol. When the amount of aliphatic polycarbonate diol is 10parts by mass or more, adhesion force is properly decreased, which ispreferable. When the amount of aliphatic polycarbonate diol is 20 partsby mass or less, reaction between polyurethane diol and the curing agenteasily occurs, which is preferable.

Incidentally, in addition to polyurethane diol and aliphaticpolycarbonate diol serving as main agent components, in the main agent,as necessary, a tackifier, a stabilizer, a filler, a plasticizer, asoftening point improver, a catalyst, or the like can be mixed asadditives. Examples of the tackifier include a rosin-based resin and aterpene-based resin. Examples of the stabilizer include an antioxidantand an ultraviolet ray inhibitor. Examples of the filler include aninorganic filler.

[Curing Agent]

As the curing agent which can be used in the infrared-light-transmittingdark color ink, for example, a curing agent having a polyisocyanatecompound as a main component is mentioned. The polyisocyanate compoundis a compound having two or more isocyanate groups in one molecule. Thisisocyanate group reacts with a hydroxyl group in the polyurethane diolcompound of the main agent to crosslink the polyurethane diol compound.Such a polyisocyanate compound is not particularly limited as long as itcan cross ink the polyurethane diol compound of the main agent. Forexample, polyurethane diisocyanate, hexamethylene diisocyanate(hereinafter, “HDI”), isocyanurate-modified isophorone diisocyanate(hereinafter, “nurate-modified IPDI”), and the like can be exemplified.Among these polyisocyanate compounds, a mixture obtained by combiningHDI and nurate-modified IPDI is preferable from the viewpoint ofimproving reactivity with a hydroxyl group. Incidentally, when a mixtureof HDI and nurate-modified IPDI is used as a curing agent, HDI andnurate-modified IPDI are preferably used in a range of 70:30 to 50:50(mass ratio).

[Blending of Main Agent and Curing Agent]

When the component of the infrared-light-transmitting dark color inkcontains a curing agent and is used for attaching base materials to eachother, the blending ratio of the main agent and the curing agent ispreferably in a range of 1.0 to 3.5 in terms of a ratio of (theisocyanate group derived from the polyisocyanate compound)/(the hydroxylgroup derived from the polyurethane diol compound), and is morepreferably in a range of 1.2 to 3.0. When the blending ratio of thepolyurethane diol compound of the main agent component and thepolyisocyanate compound of the curing agent component is in the aboverange, the infrared-light-transmitting dark color ink capable ofstrongly attaching each base material can be obtained, which ispreferable.

[Additive such as Silane Coupling Agent]

In addition to the above-described compounds, as necessary, a silanecoupling agent, a tackifier, a stabilizer, a filler, a plasticizer, asoftening point improver, a catalyst, or the like can be mixed as anadditive. Examples of the silane coupling agent may include a silanemonomer such as methyl trimethoxysilane or methyl triethoxysilane,vinylsilane such as vinyl triethoxysilane or vinyl trimethoxysilane,methacrylsilane such as 3-methacryloxypropyl triethoxysilane or3-methacryloxypropyl trimethoxysilane, and epoxy silane such as3-glycidoxy propyl trimethoxysilane or 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane. Examples of the tackifier include a rosin-based resinand a terpene-based resin. Examples of the stabilizer include anantioxidant and an ultraviolet ray inhibitor. Examples of the fillerinclude an inorganic filler.

Incidentally, the added amount of the silane coupling agent ispreferably 1% by mass to 3% by mass with respect to a total of 100 partsby mass of the main agent of the infrared-light-transmitting dark colorink and the curing agent. When the added amount of the silane couplingagent is 1% by mass or more, adhesion force is favorable, which ispreferable. When the added amount of the silane coupling agent is 3% bymass or less, durability is improved, which is preferable.

[Solvent]

In order to obtain favorable coating property and handling suitability,a solvent component is preferably added as a composition of theinfrared-light-transmitting dark color ink. As such a solvent component,the above-described carboxylic acid ester such as ethyl acetate, methylacetate, or methyl propionate can be exemplified, but the solventcomponent is not limited thereto. Incidentally, when the solvent isconfigured as a two-component type including a main agent and a curingagent, a solvent component used in the main agent and a solventcomponent used in the curing agent are independently selected and may bethe same as or different from each other.

Incidentally, the composition of the infrared-light-transmitting darkcolor ink is not limited thereto, and any composition form, including anaqueous type, a solution type, an emulsion type, a dispersion type, andthe like may be employed. The shape thereof may be any form including afilm/sheet shape, a powder, a solid, an adhesive, and the like. Further,regarding the adhesion mechanism, any mechanism type including achemical reaction type, a solvent evaporation type, a thermal meltingtype, a thermal pressure type, and the like may be employed.

<Infrared Light-Reflecting Sheet>

The infrared-light-reflecting sheet can be produced by using theinfrared-light-transmitting dark color ink. Like theinfrared-light-reflecting sheet 6 of FIG. 2, a laminate in which thetransparent adhesion layer 62, the infrared-light-transmitting darkcolor layer 60, and the reflective layer 61 are laminated can beexemplified as the infrared-light-reflecting sheet. Incidentally, theinfrared-light-reflecting sheet 6 of FIG. 2 is used as a rear surfaceprotective sheet for a solar cell module. However, the use applicationof the infrared-light-reflecting sheet of the present invention is notintended to be limited to the rear surface protective sheet for thesolar cell module. Hereinafter, each layer configuring theinfrared-light-reflecting sheet will be described.

[Infrared-Light-Transmitting Dark Color Layer]

The infrared-light-transmitting dark color layer 60 according to thepresent embodiment is a layer containing a main agent resin having ahydroxyl group, a curing agent having an isocyanate group, and a pigmentcomponent. The infrared-light-transmitting dark color layer 60 accordingto the present embodiment contains a main agent resin having a hydroxylgroup and a curing agent having an isocyanate group and has the functionof attaching sheets to each other.

The infrared-light-transmitting dark color layer 60 according to thepresent embodiment can be formed by applying or laminating theinfrared-light-transmitting dark color ink containing a curing agent,which is described above, on the reflective layer 61 and/or thetransparent adhesion layer 62 and then performing dry curing thereon. Asa coating method, the infrared-light-transmitting dark color ink can beapplied by coating methods such as a roll coating method, a gravure rollcoating method, and a kiss coating method, or a printing method.

Herein, when the infrared-light-transmitting dark color ink containingan organic dark color pigment of the related art such as anoxazine-based compound is used, in order to achieve balance among designattractiveness, infrared-light-transmitting property, and adhesivenessand adhesion stability that are necessary for a lamination member, thecoating amount thereof needs to be set to 10 g/m² or more. However, whenthe infrared-light-transmitting dark color ink containing a curing agentof the present embodiment is used, it is possible to sufficientlyachieve balance among the above with the coating amount set in a rangeof 5 g/m² to 15 g/m², more preferably 5 g/m² to 7 g/m². The reason forthis is that when the content of the pigment component is 20 parts bymass to 40 parts by mass, preferably 30 parts by mass to 40 parts bymass with respect to 100 parts by mass of the resin component, colortone can be sufficiently stabilized with a coating amount smaller thanthat, in the related art. Incidentally, this also leads to an increasein yield of the infrared-light-reflecting sheet produced by using theinfrared-light-transmitting dark color ink of the present invention andan improvement in productivity.

The brown pigment and the phthalocyanine pigment have higherdispersibility than other pigments and have a small influence onadhesiveness of the curing agent. For these reasons, a decrease inadhesiveness and adhesion stability caused by the pigment content can besuppressed. Incidentally, the thickness of theinfrared-light-transmitting dark color layer 60 is preferably in a rangeof 5 μm to 15 μm, and more preferably in a range of 5 μm to 7 μm.

[Reflective Layer]

The reflective layer 61 is formed by a resin sheet containing a whitepigment or a resin sheet having a coat layer (coating layer or printinglayer), which contains a white pigment, formed therein and is a whiteresin layer reflecting near infrared light. The reflective layer 61 hasthe function of reflecting near infrared light which has beentransmitted through the infrared-light-transmitting dark color layer 60.For this reason, for example, when the infrared-light-reflecting sheet 6of the present embodiment is used as the rear surface protective sheetfor the solar cell module, the infrared-light-reflecting sheet 6 of thepresent embodiment becomes the infrared-light-reflecting sheet (rearsurface protective sheet) 6 which can sufficiently contribute toimprovement in the electric power generation efficiency of a solar cellmodule 1. Incidentally, in the present specification, a product obtainedby processing a resin in a sheet shape is called a “resin sheet” butthis term is used as a concept also including a resin film.

As the resin sheet configuring the reflective layer 61, it is possibleto preferably use a resin sheet of a fluororesin such aspolytetrafluoroethylene (PTFE) or a copolymer of ethylene andtetrafluoroethylene (ETFE), a polyester-based resin such aspoly(meth)acrylic resin or polyethylene terephthalate (PET), and thelike. Herein, in the present embodiment, since the reflective layer 61is disposed as the outermost layer of the solar cell module 1, highweather resistance, barrier properties, and hydrolysis resistance arerequired. From such a viewpoint, among them, a fluororesin representedby ETFE or a polyester-based resin represented by PET is particularlypreferably used.

The reflective layer 61 needs to have the function of reflecting nearinfrared light. For this reason, a white resin layer containing a whitepigment having a particle diameter of 0.5 μm to 1.5 μm is preferablyused, and the particle diameter is more preferably 0.8 μm to 1.2 μm. Inthe reflective layer 61, it is preferable that the content of theparticles having a particle diameter of 0.8 μm to 1.2 μm of the whitepigment is 80% by mass or more of the particles of the entire whitepigment. When the particle diameter and the distribution ratio of thewhite pigment are adjusted to the above ranges, the white resin layercan efficiently reflect near infrared light. When theinfrared-light-reflecting sheet of the present invention is used as therear surface protective sheet for the solar cell module, the whitepigment, contributes to improvement in the electric power generationefficiency of the solar cell module. The expression “reflecting nearinfrared light” means the function in which the integrated reflectionrate in a wavelength range of about 750 nm to 2200 nm is 85% or more.

A representative example of the white pigment having a particle diameterof 0.5 μm to 1.5 μm is titanium oxide, and also in the presentinvention, titanium oxide is preferably used as the white pigment.Herein, titanium oxide also includes surface-treated titanium oxide. Forexample, when the white pigment having the above particle diameter rangeis titanium oxide, the production thereof can be performed as follows.

Aqueous titanium oxide is used as a raw material, 0.1% by mass to 0.5%by mass of aluminum compound in terms of aluminum oxide, 0.1% by mass to0.5% by mass of potassium compound in terms of potassium carbonate, and0.2% by mass to 1.0% by mass of zinc compound in terms of zinc oxidewith respect to the titanium oxide content are added to the aqueoustitanium oxide, and the resultant mixture is dried and roasted so that awhite pigment having the above particle diameter range which is mainlyformed by titanium oxide can be produced.

As the production method of the reflective layer 61, for example, amethod in which a coat layer containing a white pigment is formed on aresin sheet, and a method in which a white pigment is kneaded into aresin sheet are mentioned. There is no particular limitation to bothmethods, and the reflective layer can be produced by methods of therelated arts.

When a coat layer (coating layer or printing layer) containing a whitepigment is formed on a resin sheet, a general vehicle for coating or forink is used as a main component and the white pigment is added thereto.Further, as necessary, an ultraviolet absorbent, a cross-linking agent,or other additives are arbitrarily added to prepare a composition forcoating or for ink, the composition is applied or printed on a surfaceof a base film by using a general coating method or a printing method,and the coating layer or printing layer thereof can be formed.

When the white pigment is kneaded into a resin sheet, a resinconfiguring the resin sheet is used as a main component and the whitepigment is added thereto. Further, as necessary, other additives arearbitrarily added to prepare a resin composition, and a sheet obtainedsubjecting the white pigment to kneading processing can be produced, forexample, by a film molding method such as an extruding method or a T diemethod.

[Transparent Adhesion Layer]

The transparent adhesion layer 62 according to the present embodiment isa layer which transmits near infrared light and is disposed as theoutermost layer of the infrared-light-reflecting sheet 6. Thetransparent adhesion layer 62 is a layer having adhesion with anotherresin layer, and for example, is a layer having adhesiveness with anethylene-vinyl acetate copolymer resin (EVA resin) or a resin layercontaining polyolefin such as polyethylene. For this reason, like thetransparent adhesion layer 62 of FIG. 2, a rear surface sealing materiallayer 5 and the transparent adhesion layer 62 can be laminated to bebrought into close contact with each other.

It is required that the transparent adhesion layer 62 according to thepresent embodiment transmits near infrared light reflected by thereflective layer 61 or is transparent or translucent depending on therequirements of design attractiveness. From such a viewpoint, apolyethylene resin, a polyolefin resin such as a polypropylene resin,and polyethylene terephthalate (PET) are preferably used for thetransparent adhesion layer 62.

[Other Layers]

In the infrared-light-reflecting sheet 6 of the present embodiment,other layers may be provided within a range not impairing the effects ofthe present invention. For example, a weather resistance layer (notillustrated) formed by a fluororesin, polyethylene terephthalate (PET),or the like may be further laminated on the side opposite to thelamination surface of the transparent adhesion layer 62 of thereflective layer 61, that is, on the outermost side of theinfrared-light-reflecting sheet 6. In this case, in order to improvedesign attractiveness, the weather resistance layer may be darklycolored. Alternatively, for example, another transparent reinforcementlayer (not illustrated) for increasing the strength of the rear surfaceprotective sheet 6 may be provided between the reflective layer 61 andthe transparent adhesion layer 62.

An infrared-light-transmitting coat layer containing an organic darkcolor pigment may be further laminated on the surface opposite to thelamination surface of the infrared-light-transmitting dark color layer60 of the reflective layer 61. When the infrared-light-transmitting darkcolor layer and the infrared-light-transmitting coat layer are laminatedrespectively, both surfaces of the infrared-light-reflecting sheet canbe unified with a dark color. Since the infrared-light-reflecting sheetof the present embodiment is the infrared-light-reflecting sheet inwhich both surfaces are unified with a dark color, theinfrared-light-reflecting sheet of the present embodiment is preferablein terms of design attractiveness.

Further, when the infrared-light-transmitting coat layer according tothe present embodiment is formed to be a layer transmitting nearinfrared light having a wavelength of 750 nm to 1500 nm similarly to theinfrared-light-transmitting dark color layer 60, heat generation causedby absorption of near infrared light having a wavelength of 750 nm to1500 nm can be suppressed.

Specific examples of the organic dark color pigment contained in theinfrared-light-transmitting coat layer include oxazine, benzimidazolone,pyrrole, quinacridone, azo, perylene, dioxane, isoindolinone,indanthrene, quinophthalone, perinone, and phthalocyanine pigments. Fromthe viewpoint of UV resistance, a dark color pigment composed of anoxazine-based organic pigment or at least one or more pigments selectedfrom the group consisting of a benzimidazolone pigment,4-[(2,5-dichlorophenyl)azo]-3-hydroxy-N-(2,5-dimethoxyphenyl)-2-naphthalenecarboxamide,1-[(4-nitrophenyl)azo]-2-naphthalenol,bis[3-hydroxy-4-(phenylazo)-2-naphthalenecarboxylic acid]copper salt, C.I. Pigment Brown 7,N,N′-bis(2,4-dinitrophenyl)-3,3′-dimethoxy-1,1′-biphenyl-4,4′-diamine,3,4,9,10-perylenetetracarboxylic diimide,Δ2,2′(1H,1′H)-binaphtho[2,1-b]thiophen-1,1′-dione, andN,N′-(10,15,16,17-tetrahydro-5,10,15,17-tetraoxo-5H-dinaphtho[2,3-a:2′,3′-i]carbazole-4,9-diyl)bis(benzamide),and a phthalocyanine pigment can be preferably used.

Incidentally, by kneading the pigment component contained in theinfrared-light-transmitting dark color ink into the base film, similarlyto the infrared-light-transmitting dark color layer 60, a dark colorfilm or dark color sheet having high design attractiveness can beproduced. This dark dolor film or dark color sheet can be used as theinfrared-light-transmitting dark color layer in a multi-layered sheet.In the production of the dark color film or dark color sheet by kneadingthe pigment component into the base film, the content of the brownpigment in the pigment component is preferably 43 parts by mass to 233parts by mass with respect to 100 parts by mass of the phthalocyaninepigment (the content ratio of the brown pigment and the phthalocyaninepigment is in a range of 30:70 to 70:30 in terms of mass ratio), andmore preferably 66 parts by mass to 150 parts by mass (the content ratioof the brown pigment and the phthalocyanine pigment is in a range of40:60 to 60:40 terms of mass ratio).

As described above, when the dark color film or dark color sheet isformed by kneading the pigment component into the base film, first, athermoplastic resin configuring the base film is used as a maincomponent, the pigment component is added thereto, and further, asnecessary, one or two or more additives such as an ultravioletabsorbent, a plasticizer, a light stabilizer, an antioxidant, anantistatic agent, a cross-linking agent, a curing agent, a filler, alubricant, a strengthening agent, a reinforcement agent, a fireretardant, a flame-resistant agent, a foaming agent, a fungicide, and acoloring agent (such as a pigment and a dye) are arbitrarily added.Further, as necessary, a solvent, a dilution agent, or the like is addedand then the resultant mixture is sufficiently kneaded to prepare athermoplastic resin composition. The thermoplastic resin compositionprepared in this way is molded, for example, by using an extruder, aT-die extruder, a cast molding machine, an inflation molding machine, orthe like according to a film molding method such as an extruding method,a T die method, a cast molding method, or an inflation method so thatthe dark color film or dark color sheet can be produced. Further, asnecessary, for example, this film or sheet can also be produced, forexample, by stretching the thermoplastic resin composition in theuniaxial or biaxial direction using a tenter system or tubular system.

When other layers are provided on the infrared-light-reflecting sheet,an adhesive layer for attaching respective layers may be formed at aplurality of positions. If each layer disposed between the transparentadhesion layer 62 and the infrared-light-transmitting dark color layer60 is transparent at this time, when an arbitrary adhesive layer at thetransparent adhesion layer side in relation to the reflective layer 61among the plurality of adhesive layers is employed as theinfrared-light-transmitting dark color layer 60, aninfrared-light-reflecting sheet with sufficient weather resistance anddurability can be obtained while the appearance is darkly colored. Whenthe infrared-light-reflecting sheet of the present embodiment isdiverted to the rear surface protective sheet for the solar cell module,the infrared-light-reflecting sheet of the present embodiment can beemployed as the rear surface protective sheet which can sufficientlycontribute to an improvement in electric power generation efficiency ofthe solar cell module. Such an infrared-light-reflecting sheet (rearsurface protective sheet) is also in the scope of the present invention.

[Rear Surface Protective Sheet for Solar Cell Module]

A preferred usage example of the infrared-light-reflecting sheet of thepresent embodiment will be described. For example, when theinfrared-light-reflecting sheet 6 of the present embodiment is disposedat a non-photoreception surface side of the solar cell element of thesolar cell module, the infrared-light-reflecting sheet 6 of the presentembodiment can be used as a rear surface protective sheet for a solarcell module. FIG. 1 is a sectional schematic view illustrating anexample of a layer structure of a solar cell module. The solar cellmodule 1 configuring a solar cell has a configuration in which atransparent front substrate 2, a front surface sealing material layer 3,a solar cell element 4 the rear surface sealing material layer 5, andthe rear surface protective sheet (infrared-light-reflecting sheet) 6are laminated from a photoreception surface side of incident light 7 asillustrated in FIG. 1.

The rear surface protective sheet will be described by means of FIG. 2.The rear surface protective sheet 6 includes theinfrared-light-transmitting dark color layer 60, the reflective layer61, and the transparent adhesion layer 62. The reflective layer 61 andthe transparent adhesion layer 62 are attached to each other with theinfrared-light-transmitting dark color layer 60 interposed therebetween.In the solar cell module 1, the reflective layer 61 is disposed on theoutermost layer side of the module, and the transparent adhesion layer62 is disposed on the inner layer side of the module, that is, on therear surface sealing material layer 5 side.

Herein, generally, most of sealing materials for solar cell modules aretransparent or translucent. Therefore, when the solar cell module 1 isseen from the transparent front substrate 2 side, regarding a gapportion in which the solar cell element 4 is not disposed, the color ofthe infrared-light-transmitting dark color layer 60 is seen through thetransparent adhesion layer 62. The surface of the solar cell element 4black or has a dark color close to black in many cases. In particular,regarding thin film solar cell elements for which there is an increasingdemand recently, surfaces of most products are black or have a darkcolor close to black. Since the infrared-light-transmitting dark colorlayer 60 is black or has a dark color close to black, the rear surfaceprotective sheet 6 enables the appearances of a lot of solar cellmodules, that is, the appearances of thin film solar cell modulesmounted with thin film solar cell elements to be unified with black or adark color close to black, and thus the solar cell modules can beconfigured as preferable solar cell modules in terms of designattractiveness.

In order to unify the appearance of the rear surface protective sheet(infrared-light-reflecting sheet) 6 with black or a dark color close toblack, for example, a color difference ΔE*ab between a color tone of theinfrared-light-transmitting dark color layer 60 and a color tone ofcarbon black as measured under the conditions of a D65 light source anda 10° view angle according to JIS-Z 8722 is preferably 10 or less andmore preferably 7 or less.

Sunlight which is not absorbed in the solar cell element 4 is incidentto the rear surface protective sheet 6 from the transparent adhesionlayer 62 side. Most near infrared light included in sunlight transmitsthrough the infrared-light-transmitting dark color layer 60 withoutbeing absorbed in the infrared-light-transmitting dark color layer 60,and thus reaches the reflective layer 61. Since the reflective layer 61reflects near infrared light, most of infrared light which has reachedthe reflective layer 61 is reflected to return to theinfrared-light-transmitting dark color layer 60. The reflected infraredlight transmits through the infrared-light-transmitting dark color layer60 and is further reflected to be absorbed in the solar cell element 4.The infrared-light-transmitting dark color layer 60 does not absorbinfrared light, and thus heat generation caused by absorption of nearinfrared light can be suppressed. As a result, a decrease in electricpower generation efficiency caused by heat generation of the solar cellmodule 1 can be prevented.

Further, the infrared-light-transmitting dark color ink of the presentinvention contains the brown pigment and the phthalocyanine pigment at apredetermined ratio. For this reason, a transmission rate of nearinfrared light is even higher than in the case of using theinfrared-light-transmitting dark color ink of the related art.Accordingly, absorption of near infrared light is suppressed to suppressan increase in temperature of the solar cell module, and the electricpower generation efficiency of the solar cell module can be furtherincreased by using infrared light in power generation. Therefore, theelectric power generation efficiency of the solar cell module using theinfrared-light-reflecting sheet of the present invention as the rearsurface protective sheet is further improved.

Incidentally, in the thin film solar cell module, the suppression ofheat generation of all constituents in the module does not necessarilycontribute to an improvement in electric power generation efficiency,but the surface temperature of the solar cell element that is black orhas a dark color is preferably increased to 50° C. to 70° C. withreference to the relation with the annealing effect. When theinfrared-light-reflecting sheet of the present embodiment is used as therear surface protective sheet, in order to satisfy the demand related todesign attractiveness, while the appearance of theinfrared-light-reflecting sheet is defined to be black or have a darkcolor close to black, the near infrared light reflected by thereflective layer 61 is not accumulated inside the rear surfaceprotective sheet 6 but the near infrared light can be absorbed by thesolar cell element 4 without any loss. According to this, it is possibleto efficiently increase the surface temperature of the thin film solarcell element that is black or has a dark color to the above-describedtemperature. Also from such a viewpoint, the infrared-light-reflectingsheet of the present invention can particularly preferably be used asthe rear surface protective sheet of the thin film solar cell module.

[Production Method of Rear Surface Protective Sheet for Solar CellModule]

The rear surface protective sheet 6 can be produced by providing theinfrared-light-transmitting dark color layer 60 between the reflectivelayer 61 and the transparent adhesion layer 62 and then performing drylamination processing on the obtained product. Incidentally, byproviding other layers, even when the adhesive layer includes aplurality of layers, respective layers can be brought into close contactwith each other to be laminated.

[Production Method of Solar Cell Module]

As the production method of the solar cell module 1 constituting thesolar cell, a method of sequentially laminating respective membersconstituting the solar cell and integrating the obtained product byvacuum heat lamination processing can be used. The laminationtemperature at this time is preferably set in a range of 130° C. to 190°C. The lamination time is preferably in a range of 5 minutes to 60minutes, and particularly preferably in a range of 8 minutes to 40minutes. In this way, the respective members constituting the solar cellare integrated and thermally pressed so that the solar cell module 1 canbe produced.

<Another Embodiment of Infrared-Light-Reflecting Sheet >

Another embodiment of the infrared-light-reflecting sheet of the presentinvention will be described by means of FIG. 6. (Incidentally, asnecessary, for distinguishing from the infrared-light-reflecting sheet 6of the present embodiment in FIG. 6, the infrared-light-reflecting sheetin which the infrared-light-transmitting dark color layer including theinfrared-light-transmitting dark color layer 60 has the function ofattaching sheets to each other is laminated, like theinfrared-light-reflecting sheet 6 of FIG. 2 is described as the“infrared-light-reflecting sheet of the above-described embodiment.) Theinfrared-light-transmitting dark color layer 60 of theinfrared-light-reflecting sheet of the present embodiment is theinfrared-light-transmitting dark color layer 60 not having the functionof attaching sheets to each other, and two layers among layers laminatedbetween the transparent adhesion layer 62 and the reflective layer 61are the infrared-light-transmitting dark color layer 60 and thetransparent adhesive layer 63. From the viewpoint of designattractiveness, there is a case where the entire surface of the sheet isnot darkly colored, but an infrared-light-reflecting sheet partiallycolored is required, for example, for providing a design such aspatterning. When such an infrared-light-reflecting sheet is produced,for example, the infrared-light-transmitting dark color ink having aninfrared-light-transmitting property is partially applied to a resinsheet such as the transparent adhesion layer and/or the reflective layerin advance, and the infrared-light-transmitting dark color ink partiallyapplied in this way is cured to form the infrared-light-transmittingdark color layer 60. Thereafter, a transparent adhesive not mixed with apigment is applied and cured to form a transparent adhesive layer, andthe reflective layer and the transparent adhesion layer are laminated.By performing lamination in this way, an infrared-light-reflecting sheethaving a design such as patterning can be produced by performing partialcoloring.

Even in the case of the infrared-light-reflecting sheet in which aninfrared-light-transmitting dark color layer and a transparenteasy-adhesive layer transmitting all light beams are laminated in thisorder on the surface of the reflective layer instead of the transparentadhesion layer 62 and the transparent adhesive layer 63, theinfrared-light-transmitting dark color layer 60 is formed by partiallyapplying the infrared-light-transmitting dark color ink to thereflective layer and curing the infrared-light-transmitting dark colorink so that the infrared-light-reflecting sheet having a design such aspatterning can be produced similarly. When the transparent easy-adhesivelayer is laminated instead of the transparent adhesive layer and thetransparent adhesion layer, the number of layers of theinfrared-light-reflecting sheet can be decreased, which is preferable interms of productivity.

Since the infrared-light-transmitting dark color layer 60 is formed bythe infrared-light-transmitting dark color ink, theinfrared-light-transmitting dark color layer 60 transmits near infraredlight. Since the transparent adhesive layer does not contain a pigmentabsorbing infrared light, the transparent adhesive layer also transmitsnear infrared light. The reflective layer reflecting near infrared lighthaving a wavelength of 750 nm to 1500 nm can reflect near infrared lightwhich has been transmitted through the infrared-light-transmitting darkcolor layer 60 and the transparent adhesive layer. For this reason, alsowhen the infrared-light-reflecting sheet of this embodiment is used asthe rear surface protective sheet for the solar cell module, nearinfrared light which has been transmitted through theinfrared-light-transmitting dark color layer 60 and the transparentadhesive layer can be also used again for electric power generation (seeFIG. 6). When the infrared-light-reflecting sheet of the presentembodiment is used as the rear surface protective sheet for the solarcell module, the rear surface protective sheet becomes an excellentsolar cell module rear surface protective sheet which is also excellentin terms of design attractiveness and can maintain electric powergeneration efficiency as high as that in the related art.

[Infrared-Light-Transmitting Dark Color Layer]

Hereinafter, the infrared-light-reflecting sheet in this embodiment willbe described while focusing on specific portion of this embodiment. Theinfrared-light-transmitting dark color layer 60 is manly disposed as alaminate between the reflective layer 61 and the transparent adhesionlayer 62. The infrared-light-transmitting dark color layer 60 may belaminated on the entire surface of the transparent adhesion layer and/orthe reflective layer or may be laminated only on a part of the surfaceof the transparent adhesion layer and/or the reflective layer. Theinfrared-light-reflecting sheet in which the infrared-light-transmittingdark color layer 60 is laminated only on a part of the surface of thetransparent adhesion layer and/or the reflective layer is aninfrared-light-reflecting sheet with high design attractiveness.Incidentally, this infrared-light-transmitting dark color layer 60 maybe attached, for example, to the transparent adhesion layer 62 asillustrated in FIG. 6, or in addition to a case other than the caseillustrated in FIG. 6, may be laminated on the inner side of thereflective layer 61 while the infrared-light-transmitting dark colorlayer 60 is in contact with the reflective layer 61 as long as theinfrared-light-transmitting dark color layer 60 is disposed at thephotoreception surface side in relation to the reflective layer 61.

In the infrared-light-reflecting sheet of the present embodiment,similarly to the infrared-light-reflecting sheet of the above-describedembodiment, the infrared-light-transmitting dark color layer 60 isconfigured by a cross-linked resin in which the main agent resin havinga hydroxyl group (hereinafter, also simply referred to as “main agentresin”) is cross-linked by an isocyanate-based curing agent. Theinfrared-light-transmitting dark color layer 60 can be formed byapplying the infrared-light-transmitting dark color ink, which containsthe main agent resin, the curing agent, the solvent, and the pigmentcomponent containing the brown pigment and the phthalocyanine pigment,to the surface of the resin sheet and drying and curing the appliedinfrared-light-transmitting dark color ink.

In the case of the infrared-light-transmitting dark color ink formingthe infrared-light-transmitting dark color layer on the surface of thetransparent adhesion layer and/or the reflective layer like theinfrared-light-transmitting dark color ink of the present embodiment,the content of the pigment component is preferably 20 parts by mass to50 parts by mass with respect to 100 parts by mass of the resincomponent in the main agent, and more preferably 35 parts by mass to 45parts by mass. When the content of the pigment component is adjusted inthis range, the color tone can be further stabilized. Since theinfrared-light-transmitting dark color layer 60 can be formed by a smallamount of the infrared-light-transmitting dark color ink, even when theinfrared-light-transmitting dark color layer 60 is laminated only on apart of the surface of the resin sheet, a step difference between thesurface on which the infrared-light-transmitting dark color layer 60 islaminated and the surface on which the infrared-light-transmitting darkcolor layer 60 is not laminated becomes small. For this reason, thetransparent adhesion layer 62 and the reflective layer 61 can belaminated with a small amount of transparent adhesive via thetransparent adhesive layer 63, and thus the infrared-light-reflectingsheet can be produced in low costs. Even in the case of theinfrared-light-reflecting sheet in which the infrared-light-transmittingdark color layer and the transparent easy-adhesive layer transmittingall light beams are laminated in this order on the surface of thereflective layer instead of the transparent adhesion layer 62 and thetransparent adhesive layer 63, lamination can be carried out with asmall amount of a primer agent via other layers such as the reflectivelayer 61 and the rear surface sealing material layer 5. For this reason,the infrared-light-reflecting sheet can be produced at low cost.

In the production process of the infrared-light-reflecting sheet of thepresent embodiment, the resin sheet on which theinfrared-light-transmitting dark color layer is formed is exposed on theoutermost surface once in the pre-process of applying a transparentadhesive or a primer agent. For this reason, theinfrared-light-transmitting dark color layer according to the presentembodiment having no function of attaching sheets to each other requiresblocking resistance.

Regarding the blending ratio of the main agent and the curing agent inthe infrared-light-reflecting sheet of the present embodiment, a NCO/OHratio that is a ratio of an NCO value of the curing agent to an OH valueof the main agent resin is in a range of 1.0 to 2.0. When the NCO/OHratio is set to 2.0 or less, blocking resistance of theinfrared-light-transmitting dark color layer 60 can be improved. Whenthe NCO/OH ratio is set to 1.0 or more, adhesion between theinfrared-light-transmitting dark color layer 60 and the resin sheet canbe improved.

From the viewpoint of adhesion between the infrared-light-transmittingdark color layer 60 and the resin sheet and blocking resistance of theinfrared-light-transmitting dark color layer 60, whenpolyurethane/polycarbonate diol-based component is used as the mainagent component of the resin component, the number average molecularweight of polyurethane diol is preferably 6000 to 8000 and the hydroxylgroup value of polyurethane diol is preferably 15 mgKOH/g. As the curingagent, a mixture of an isocyanurate-modified product of hexamethylenediisocyanate (HDI nurate product) and a TMP adduct-modified product ofisophorone diisocyanate (IPDI) at a ratio of 1:1 (mass ratio) ispreferably used.

A coating amount of the infrared-light-transmitting dark color ink inthe infrared-light-reflecting sheet of the present embodiment ispreferably in a range of 3 g/m² to 7 g/m². When the coating amount ofthe infrared-light-transmitting dark color ink is set to 3 g/m² or more,the color tone of the infrared-light-transmitting dark color layer 60can be made sufficient. When the coating amount of theinfrared-light-transmitting dark color ink is set to 7 g/m² or less, astep difference between the surface on which theinfrared-light-transmitting dark color layer 60 is laminated and thesurface on which the infrared-light-transmitting dark color layer 60 isnot laminated becomes small. For this reason, the reflective layer 61and the transparent adhesion layer 62 can be laminated with a smallamount of a transparent adhesive via the transparent adhesive layer 63,and thus the infrared-light-reflecting sheet can be produced at lowcost.

[Transparent Adhesive Layer]

The transparent adhesive layer 63 is an adhesive layer provided mainlyfor attaching the reflective layer 61 and the transparent adhesion layer62 to each other. In the present embodiment, the transparent adhesivelayer 63 is formed by curing the transparent adhesive applied to theupper surface of the reflective layer 61 or the lower surface of thetransparent adhesion layer 62 facing the upper surface after lamination.

The transparent adhesive layer 63 requires sufficient adhesiveness andadhesiveness durability. Further, in order to reflect near infraredlight, the transparent adhesive layer 63 preferably has a property oftransmitting this near infrared light.

A transparent adhesive having a characteristic of transmitting lighthaving a wavelength of 750 nm to 1500 nm in a state of being curedsimilarly to the infrared-light-transmitting dark color ink of thepresent embodiment is preferably used for the transparent adhesiveforming the transparent adhesive layer 63.

The adhesive composition used in the transparent adhesive layer 63 is,similarly to the infrared-light-transmitting dark color ink of thepresent embodiment, preferably a two-component type including the mainagent and the curing agent, and from the viewpoint of coating propertyand handling property, a solvent is suitably contained in thecomposition.

The main agent resin component of the transparent adhesive used in thetransparent adhesive layer is, similarly to theinfrared-light-transmitting dark color ink of the present embodiment,preferably a polyurethane/polycarbonate diol-based component containinga mixture of polyurethane diol and aliphatic polycarbonate diol, whenthe mixture obtained by blending a predetermined amount of a specificpolyurethane diol and aliphatic polycarbonate diol is used as the mainagent, adhesiveness and weather resistance of the transparent adhesivelayer are improved.

The adhesive composition used in the transparent adhesive layer 63according to the present embodiment contains the main agent and thecuring agent as main components. The blending ratio of the main agentand the curing agent may be the same as in theinfrared-light-transmitting dark color ink used in theinfrared-light-reflecting sheet of the above-described embodiment. Whenthe blending ratio of the polyurethane diol compound of the main agentcomponent and the polyisocyanate compound of the curing agent componentis set in the above range, an adhesive capable of strongly attachingeach base material can be obtained, which is preferable. Incidentally,in addition to the above-described compound, as necessary, a silanecoupling agent, a tackifier, a stabilizer, a filler, a plasticizer, asoftening point improver, a catalyst, or the like can be mixed as anadditive.

In order to obtain favorable coating property and handling suitability,a solvent component is preferably added to the transparent adhesivecomposition. As such a solvent component, the above-described carboxylicacid ester such as ethyl acetate, methyl acetate, or methyl propionatecan be exemplified, but the solvent component is not limited thereto.Incidentally, as already described, the adhesive is configured as atwo-component type including the main agent and the curing agent, but asolvent component used in the main agent and a solvent component used inthe curing agent are independently selected and may be the same as ordifferent from each other.

Incidentally, the transparent adhesive composition is not limitedthereto, and any composition form of an aqueous type, a solution type,an emulsion type, a dispersion type, and the like may be employed. Theshape thereof may be any form of a film/sheet shape, a powder, a solid,and the like. In addition, regarding the adhesion mechanism, any mode ofa chemical reaction type, a solvent evaporation type, a thermal meltingtype, a thermal pressure type, and the like may be employed.

The transparent adhesive layer 63 can be formed, for example, byapplying or laminating the adhesive composition, which is describedabove, on the reflective layer 61 and/or the transparent adhesion layer62 and then performing dry curing thereon.

[Transparent Adhesion Layer]

The same transparent adhesion layer as the layer used in the transparentadhesion layer used in the infrared-light-reflecting sheet of theabove-described embodiment can be used as the transparent adhesion layeraccording to the present embodiment. A film or sheet produced by a filmmolding method such as an extruding method or a T die method may be usedas the transparent adhesion layer according to the present embodiment.

[Transparent Easy-Adhesive Layer]

Instead of the transparent adhesive layer and the transparent adhesionlayer, the transparent easy-adhesive layer may be formed between therear surface sealing material layer 5 and theinfrared-light-transmitting dark color layer 60. The transparenteasy-adhesive layer is a so-called primer layer, a primer compositionconfiguring the transparent easy-adhesive layer contains, for example,an olefin-based resin and an aqueous medium, and a primer compositionsubstantially not containing an organic solvent can be used. When thetransparent easy-adhesive layer is laminated instead of the transparentadhesive layer and the transparent adhesion layer, the number of layersof the infrared-light-reflecting sheet can be decreased, which ispreferable in terms of productivity.

The olefin-based resin contained in the primer composition used forforming the transparent easy-adhesive layer (hereinafter, also simplyreferred to as “primer composition”) is preferably an acid-modifiedpolyolefin resin containing an olefin component and an unsaturatedcarboxylic acid component. The acid-modified polyolefin resin preferablyhas an MFR at 190° C. and a load of 2.16 kg as measured according to JISK7210 of 0.01 g/10 min or more and less than 100 g/10 min. According tothis, it is possible to form the transparent adhesion layer 62 whichmaintains favorable dispersibility in the aqueous medium at the stage ofthe primer composition and is excellent in adhesiveness to theolefin-based resin forming the rear surface sealing material layer 5.

For example, a primer composition described in JP 2013-74172 A can beused as the primer composition. Strong adhesiveness can be exhibitedbetween the rear surface sealing material layer 5 and theinfrared-light-transmitting dark color layer.

[Other Layers]

In the infrared-light-reflecting sheet of the present embodiment,similarly to the infrared-light-reflecting sheet of the above-describedinfrared-light-reflecting sheet, other layers may be provided within arange not impairing the effects of the present invention.

[Rear Surface Protective Sheet for Solar Cell Module]

The infrared-light-reflecting sheet of the present embodiment can beproduced, for example, by using the reflective layer 61 or transparentadhesion layer 62 having the infrared-light-transmitting dark colorlayer 60 laminated thereon in advance and performing dry laminationprocessing therebetween via the transparent adhesive layer 63.Incidentally, by providing other layers, even when the transparentadhesive layer includes a plurality of layers, respective layers arebrought into close contact with each other to be laminated in thesimilar method.

[Solar Cell Module]

In the infrared-light-reflecting sheet of the present embodiment,similarly to the production method of the solar cell module, respectivemembers configuring the solar cell are sequentially laminated. Forexample, the solar cell module can be produced by performing vacuum heatlamination processing to integrate the respective members.

A usage example in which the infrared-light-reflecting sheet in whichthe surface can be partially colored is used as the rear surfaceprotective sheet for the solar cell module like theinfrared-light-reflecting sheet of the present embodiment will bedescribed. Since most of sealing materials for solar cell modules aretransparent or translucent, the color of the rear surface protectivesheet 6 for the solar cell module can be recognized in a gap portion inwhich the solar cell element 4 is not disposed (non-element region) inplan view from the surface side in which the solar cell element isdisposed. By using the infrared-light-reflecting sheet of the presentembodiment, in plan view, when an element region gap portion(non-element region) is colored, the element region gap portion can be adark color region having an average reflection rate of 10% or less in awavelength range of 400 nm to 700 nm. When the element region in whichthe solar cell element is disposed is not colored, the element regioncan be a reflection region having an average reflection rate of 80% ormore in. a wavelength range of 1000 nm to 1200 nm.

EXAMPLES

Hereinafter, the present invention will be described in more detail bymeans of Examples and Comparative Examples. However, the presentinvention is not limited to the following Examples and the like.

For evaluating a near infrared light transmission rate, colorcoordinate-coating amount dependency, high-temperature discolorationproperty, adhesiveness, and adhesiveness durability of theinfrared-light-transmitting dark color ink according to the presentembodiment, each ink was produced by the following method and aninfrared-light-reflecting sheet using the ink and a pseudo module samplewere produced.

[Main Agent]

Ethylene glycol (32.3 parts by mass), 2,2-dimethyl-1,3-propanediol(270.8 parts by mass), 1,6-hexanediol (122.9 parts by mass), adipic acid(228.1 parts by mass), and isophthalic acid (664 parts by mass) wereadded to a flask equipped with a stirrer and a nitrogen gas introducingtube in a nitrogen atmosphere, the resultant mixture was subjected tonitrogen bubbling at 180° C. to 220° C. and reacted until an acid valueof 2 mgKOH/g is reached, and then ethyl acetate (860 parts by mass) wasadded thereto, thereby obtaining a 50% polyester diol H solution. Thehydroxyl group value of the obtained resin was 32 mgKOH/g and the numberaverage molecular weight thereof was about 3500.

100 parts by mass of aliphatic polycarbonate diol having a numberaverage molecular weight of 1000 (product name “DURANOL T5651”manufactured by Asahi Kasei Chemicals Corporation, hereinafter,abbreviated as “PDC 1000”), and polyester diol H (50 parts by mass),1,6-hexanediol (2 parts by mass), isophorone diisocyanate (23.8 parts bymass), and ethyl acetate (175.8 parts by mass) which are described abovewere added to a flask equipped with a stirrer in a nitrogen atmosphere,and the resultant mixture was heated to reflux until isocyanateabsorption at 2270 cm⁻¹ disappeared in the infrared absorption spectrum,thereby obtaining a 50% polyurethane diol solution. The hydroxyl groupvalue of the obtained resin was 14 mgKOH/g and the number averagemolecular weight thereof was about 8000.

A main agent was prepared by mixing 100 parts by mass of polyurethanediol and 15 parts by mass of aliphatic polycarbonate diol (B) (PDC1000), which are described above.

[Curing Agent]

A mixture of hexamethylene diisocyanate (HDI adduct: bifunctional) andisocyanurate-modified isophorone diisocyanate (nurate-modified IPDI) wasused. The mixing ratio of the adduct-modified HDI and thenurate-modified IPDI, that is, (HDI adduct)/(nurate-modified IPDI) wasset to 6:4 (mass ratio).

[Infrared-Light-Transmitting Dark Color Ink (Ink 1)]

Pigment: brown pigment (benzimidazolone pigment (Pigment Brown 25,particle diameter: 0.08 μm)), phthalocyanine pigment (amorphousphthalocyanine blue pigment (Pigment Blue 15, particle diameter: 0.15 to0.20 μm))

Solvent: ethyl acetate

Ink 1 was prepared by dissolving the main agent (solid contentproportion: 50% by mass), the curing agent (solid content proportion:10% by mass), the brown pigment (benzimidazolone pigment), and thephthalocyanine pigment (amorphous phthalocyanine pigment) (the contentratio of the benzimidazolone pigment and the phthalocyanine pigment was52.5:47.5, and the content of the pigment component was 35 parts by masswith respect to 100 parts by mass of the resin component) in thesolvent.

[Dark Color Ink (Ink 2) ]

Ink 2 was prepared in a similar manner to Ink 1, except that an organicpigment was adjusted as follows and the coating amount of the solidcontent was adjusted to 10 g/m² to 20 g/m² (thickness after curing: 10μm to 20 μm). Pigment: 16.7% by mass of dioxazine compound (the contentof the pigment component was 20 parts by mass with respect to 100 partsby mass of the resin component)

(Measurement of Spectral Transmission Rate)

For evaluating the reflectivity (transmittivity) of near infrared lightof the infrared-light-transmitting dark color ink according to thepresent embodiment, transmittivity measurement samples were produced asExamples and Comparative Examples by the following method.

The following resin was used as a resin base material serving as areflective layer. Reflective layer: White PET manufactured by TORAYINDUSTRIES, INC., 188 μm The following resin was used as a resin basematerial serving as a transparent adhesion layer. Transparent adhesionlayer: polyethylene, 60 μm

<Sample Production>

Example 1

Ink 1 was gravure coated on a sheet formed by the reflective layer (thecoating amount is 5 g/m²), an adhesive layer having a thickness of 5 μm(dry state) was laminated thereon, then the transparent adhesion layerwas laminated thereon, and the obtained product was subjected to thermalcuring by performing an aging treatment at 45° C. to 55° C. for 168hours, thereby producing an infrared-light-reflecting sheet.

Comparative Example 1

Ink 2 was gravure coated on a sheet formed by the reflective layer (thecoating amount is 12 g/m²), an adhesive layer having a thickness of 12μm (dry state) was laminated thereon, then the transparent adhesionlayer was laminated thereon, and the obtained product was subjected tothermal curing by performing an aging treatment at 45° C. to 55° C. for168 hours, thereby producing an infrared-light-reflecting sheet.

<Evaluation>

A reflection rate (%) of light having a wavelength of 300 nm to 1200 nmwhen light was incident to the infrared-light-reflecting sheet samplesof Example 1 and Comparative Example 1 was evaluated by using aspectrophotometer (“U-4100” manufactured by Hitachi High-TechnologiesCorporation). Evaluation results are presented in FIG. 3.

From FIG. 3, when the infrared-light-reflecting sheet of Example 1 isprovided with the infrared-light-transmitting dark color layer 60containing a predetermined amount of the brown pigment (benzimidazolonepigment) and the phthalocyanine pigment, an infrared light transmissionrate is particularly improved near a wavelength of about 800 nm to 900nm that has higher energy than a wavelength of 1000 nm or more. For thisreason, it is found that as compared to the case of adding an organicblack pigment of the related art, the infrared-light-transmitting darkcolor ink has a high transmission rate near a wavelength of about 800 nmto 900 nm.

Incidentally, a transmission rate measurement sample was produced bypeeling off polyethylene and the white PET of theinfrared-light-reflecting sheet of Example 1 and dissolving theinfrared-light-transmitting dark color layer by using methyl ethylketone. The measurement sample was injected into a quartz glass cell,and a transmission rate (%) of light having a wavelength of 300 nm to1200 nm was measured with a spectrophotometer (for example, anultraviolet spectrophotometer “V-670” manufactured by JASCO Corporationor “U-4100” manufactured by Hitachi High-Technologies Corporation). As aresult, the transmission rate of light having a wavelength of 425 nm was11.6%, and the transmission rate of light having a wavelength of 675 nmwas 10.0%.

The infrared-light-reflecting sheet of Example 1 approximately absorbslight in a visible range (wavelength: 380 nm to 780 nm); on the otherhand, the infrared-light-reflecting sheet of Comparative Example 1reflects light in a visible range near a wavelength of 700 nm to 750 nm.For this reason, the ink of Example 1 has black appearance and isexcellent in terms of design attractiveness. However, since the ink ofComparative Example 1 transmits light in a visible range near awavelength of 700 nm to 750 nm, it is found that the ink of ComparativeExample 1 has an appearance of a dark color near violet rather thanblack and is an ink that is inferior in design attractiveness.

(Color Coordinate-Coating Amount Dependency Test 1)

<Sample Production>

Examples 2 to 4

Each infrared-light-reflecting sheet was produced by gravure coating Ink1 on each infrared-light-reflecting sheet at each coating amount,similarly to Example 1. Thereafter, each infrared-light-reflecting sheetwas used as the rear surface protective sheet to newly produce a pseudomodule.

The pseudo module was produced by vacuum lamination in such a mannerthat glass as the transparent front substrate, an ethylene-vinyl acetatecopolymer resin (EVA resin) of 450 μm as the sealing material layer, andthe sample according to this Example as the infrared-light-reflectingsheet (rear surface protective sheet) were laminated in the followingorder: transparent front substrate/the front surface sealing materiallayer/the rear surface sealing material layer/theinfrared-light-reflecting sheet (rear surface protective sheet).

(Vacuum Lamination Conditions: Temperature of 150° C., Vacuum Time of 5Minutes, Pressing Time of 9 Minutes)

Comparative Examples 2 to 6

Each infrared-light-reflecting sheet was produced by gravure coatingdark color Ink 2 at each coating amount instead of dark color Ink 1 inExamples 2 to 4. Thereafter, each infrared-light-reflecting sheet wasused as the rear surface protective sheet to newly produce a pseudomodule, similarly to Examples 2 to 4.

<Evaluation>

Measurement was carried out by irradiating each sample with a lightsource from the transparent resin layer side using a spectrophotometerCry 700d manufactured by KONICA MINOLTA, INC. according to JIS Z8722under the conditions of a D65 light source and a 10° view angle. Theresults of color coordinates obtained by this test are presented inTable 1 and FIGS. 4 and 5.

TABLE 1 Coating Ink amount a* b* L* Example 2 Ink 1  5 g/m² 2.06 −2.678.14 Example 3 Ink 1  7 g/m² 2.08 −2.31 — Example 4 Ink 1 10 g/m² 2.05−1.84 — Comparative Ink 2 10 g/m² 5.9 −6.3 — Example 2 Comparative Ink 213 g/m² 3.8 −3.2 — Example 3 Comparative Ink 2 15 g/m² 3.3 −2.6 8.30Example 4 Comparative Ink 2 18 g/m² 2.5 −1.2 — Example 5 Comparative Ink2 20 g/m² 1.8 −0.5 — Example 6 Carbon black  5 g/m² 0.15 −0.48 5.70

From Table 1 and FIGS. 4 and. 5, the samples of Comparative Exampleshaving a coating amount of 10 to 20 g/m² have large fluctuation in a*and b*; on the other hand, the samples of Examples have smallfluctuation in color tone for each coating amount. From Table 1, thevalue of L* of Comparative Example 4 having a coating amount of 15 g/m²is approximately equal to the value of L* of Example 2 having a coatingamount of 5 g/m². From this result, the infrared-light-transmitting darkcolor inks of Examples have a color tone close to that of carbon black,and fluctuation in color coordinate with respect to the coating amountof solid contents in the adhesive is small. For this reason, it is foundthat the infrared-light-transmitting dark color inks of Examples are aninfrared-light-transmitting dark color ink with a high yield and highproductivity. It is found that as compared to the samples of ComparativeExamples, the infrared-light-transmitting dark color inks of Examplesare an infrared-light-transmitting dark color ink which can exhibitsufficient design attractiveness even with a small coating amount.

(Color Coordinate-Coating Amount Dependency Test 2)

A pseudo module was produced as the color coordinate-coating amountdependency test 1 described above by adjusting the blending ratio (themass ratio) of the ink in which the content ratio of the brown pigment(benzimidazolone pigment (in Table 2, described as brown)) and thephthalocyanine pigment (in Table 2, described as blue) of Ink 1 waschanged as presented in Table 2 to have a coating amount of 5 g/m².Then, measurement was carried out by irradiating each sample with alight source from the transparent resin layer side using aspectrophotometer CM-700d manufactured by KONICA MINOLTA, INC. accordingto JIS Z8722 under the conditions of a D65 light source and a 10° viewangle. From the measurement result, color differences (ΔE*ab) withcarbon black were obtained respectively. The measurement result of thecolor coordinate and color differences (ΔE*ab) with carbon blackobtained by this test are presented in Table 2. Incidentally, thedescription “Content of brown pigment” in Table 2 means the content ofthe brown pigment with respect to 100 parts by mass of thephthalocyanine pigment.

The transmission rates (%) of light having a wavelength of 425 nm andlight having a wavelength of 675 nm of each ink of Examples 5 to 9, 16,and 17 and Comparative Examples 11 and 12 in Table 2 were obtainedrespectively. Specifically, 5 g/m² of each ink of Examples 5 to 9 andTest Examples 1 to 4 was gravure coated on a fluorine film (fluorinefilm AFLEX manufactured by ASAHI GLASS CO., LTD., 100 μm) serving as atransparent base material, the same transparent base material waslaminated thereon, and the obtained product was subjected to drylamination and then subjected to thermal curing by performing an agingtreatment at 45° C. to 55° C. for 168 hours, thereby producing atransmission rate measurement sample. Then, the transmission rate oflight having a wavelength of 425 nm and the transmission rate of lighthaving a wavelength of 675 nm were obtained respectively from thetransmission rate (%) of light having a wavelength of 300 nm to 1200 nmby using a spectrophotometer (“U-4100” manufactured by HitachiHigh-Technologies Corporation).

TABLE 2 Transmission Transmission Brown Blue rate of light rate of lightContent of Color having having brown difference wavelength wavelengthpigment a* b* L* (ΔE*ab) of 425 nm of 675 nm Comparative 100 0 35.1428.30 20.98 47.81 2.5 73.0 Example 11 — Example 6 80 20 10.75 7.20 9.6313.67 7.6 32.5 400 parts by mass Example 5 70 30 5.18 4.66 6.76 7.27 9.319.9 233 parts by mass Example 6 60 40 3.28 1.35 5.91 3.63 11.0 13.1 150parts by mass Example 7 50 50 2.63 −0.80 6.42 2.60 13.3 8.7 100 parts bymass Example 8 40 60 2.67 −5.24 7.43 5.66 16.4 6.0 66 parts by massExample 9 30 70 1.72 −8.25 9.16 8.65 22.1 4.4 43 parts by mass Example17 20 80 0.41 −10.29 10.04 10.73 26.9 3.7 25 parts by mass Comparative 0100 −20.63 −34.04 28.60 45.63 48.4 3.6 Example 12 0 parts by mass Carbon— — 0.15 −0.48 5.70 — — — black

From this test result, the infrared-light-transmitting dark color ink inwhich the content of the brown pigment is 43 parts by mass to 233 partsby mass with respect to 100 parts by mass of the phthalocyanine pigment(the content ratio of the brown pigment and the phthalocyanine pigmentis in a range of 30:70 to 70:30 in terms of mass ratio) and preferably66 parts by mass to 150 parts by mass (the content ratio of the brownpigment and the phthalocyanine pigment is 40:60 to 60:10 in terms ofmass ratio) has a smaller color difference (ΔE*ab) to carbon black thanthe infrared-light-transmitting dark color ink in which the content ofthe brown pigment is out of the range. For this reason, it is found thatthe infrared-light-transmitting dark color inks of Examples 5 to 9 arecloser to the color tone of carbon black than the inks of Examples 16and 17 and Comparative Examples 11 and 12, and thus are aninfrared-light-transmitting dark color ink which can exhibit sufficientdesign attractiveness.

(High-Temperature Discoloration Test)

<Sample Production>

Example 10

An infrared-light-reflecting sheet was produced by gravure coating ink 1at a coating amount of 7 g/m², similarly to Example 1. Thereafter, eachinfrared-light-reflecting sheet was used as the rear surface protectivesheet to newly produce a pseudo module, similarly to Examples 2 to 4.

Comparative Example 12

A sample was produced by gravure coating Ink 2 at a coating amount of 7g/m², similarly to Ink 1. Thereafter, pseudo modules were produced fromeach sheet sample, similarly to Examples 2 to 4.

<Evaluation>

The sample was stored at 170° C. for 14 hours, and the color tone afterstorage was measured. The color tone was obtained by measuring the colorcoordinate of each sample of Examples and Comparative Examples accordingto JIS X8722 under the conditions of a D65 light source and a 10 viewangle. Measurement was carried out on each sample by using aspectrophotometer CM-700d manufactured by KONICA. MINOLTA, INC.

The color one changes of Examples and Comparative Examples before andafter storage were measured three times, respectively. The changeamounts of average values thereof are presented in Table 3.

TABLE 3 Color ΔL* Δa* Δb* difference (ΔE*ab) Example 10 0.47 −0.78 −0.791.20 Comparative −1.84 11.53 2.70 11.98 Example 7

From Table 3, the color difference of the sample of Example 10 issmaller than that of the sample of Comparative Example 7. From thispoint, other layers of the laminate produced by using theinfrared-light-transmitting dark color ink of the present embodiment arenot discolored even when exposed to a harsh environment of 170° C.Therefore, it is found that the laminate obtained by laminating theinfrared-light-transmitting dark color ink of the present embodiment isan excellent laminate that has no change in design attractiveness evenin a high-temperature environment. In particular, when theinfrared-light-reflecting sheet of the present embodiment is used as therear surface protective sheet for the solar cell module, thediscoloration of the sealing layer caused by transition of the darkcolor pigment contained in the infrared-light-transmitting dark colorlayer 60 of the rear surface protective sheet to the sealing layer doesnot occur. Therefore, it is found that a solar cell module can beproduced which has no decrease in electric power generation efficiencycaused by the discoloration of the sealing layer and is excellent interms of storage stability.

(Interlayer Strength-Durability Test)

<Sample Production>

Adhesiveness measurement samples of Example 11 and Reference Examplewere produced respectively by performing attachment using Ink 1 and Ink2. Regarding the sample production, an infrared-light-reflecting sheetof Example 11 was produced by gravure coating Ink 1 in a similar mannerto Example 1 (the coating amount of Ink 1 is 5 g/m², and the thicknessis 5 μm (dry state)). An infrared-light-reflecting sheet of ReferenceExample was produced by gravure coating Ink 2 in a similar manner toComparative Example I (the coating amount of Ink 2 is 10 g/m², and thethickness is 10 μm (dry state)).

A test related to adhesiveness was performed on the samples of Example11 and Reference Example with the following method, and the adhesivenesswas evaluated on the basis of the measurement results. All test pieceshave a width of 15 mm.

(Adhesiveness Test) A peeling strength (N) of each sample of Example 11and Reference Example was obtained in a 180 degree peeling test methodaccording to JIS K6854-2 by measuring an initial value and a value aftereach durability test described below. In each sample measurement, apeeling tester (product name “TENSILON RTA-1150-H” manufactured by A&DCompany, Limited) was used and measurement was performed in peelingconditions of 50 mm/min and. 23° C.

(Wet Heat Durability (PCT) Test)

The conditions in a pressure cooker tester (HASTTEST manufactured byHIRAYAMA MANUFACTURING CORPORATION) were set to 120° C., 85% RH, and 1.6atm, and the above respective samples were input thereto for a certaintime (in Table 4, “before input” is described as 0 h, and “after inputfor 24 hours” is described as 24 h and the like). Thereafter, thepeeling test was performed three times. An average value of eachmeasurement result before input and after input for a certain time ispresented in Table 4.

TABLE 4 0 h 24 h 48 h 72 h Ink type [N/15 mm] Reference Ink 2 7.0 6.86.5 6.1 Example Example 11 Ink 1 7.1 6.5 5.3 5.2

From Table 4, it is found that the infrared-light-transmitting darkcolor ink according to Example 11 has the same adhesiveness andapproximately the same adhesiveness durability as those of the darkcolor ink according to Reference Example containing a dioxazine compoundhaving high adhesiveness durability.

From the above result, it is found that the infrared-light-transmittingdark color ink of the present embodiment is aninfrared-light-transmitting dark color ink which has higherinfrared-light-transmitting property, favorable design attractivenesseven with an extremely small coating amount, a favorable yield, andextremely high productivity while having the same adhesiveness andapproximately the same adhesiveness durability as those of the darkcolor ink containing a dioxazine compound.

For this reason, for example, the rear surface protective sheet for thesolar cell module which uses the infrared-light-reflecting sheetproduced by the infrared-light-transmitting dark color ink according tothe present invention can further suppress heat generation by absorbinginfrared light owing to the high infrared-light-transmitting propertythereof and can use a larger quantity of near infrared light in electricpower generation. Therefore, the solar cell module using theinfrared-light-transmitting dark color ink according to the presentembodiment is an extremely excellent solar cell module which can furtherimprove the electric power generation efficiency of the solar cellmodule as compared to the related art.

Examples in Other Embodiments

For evaluating adhesiveness, adhesiveness durability, blockingresistance, adhesion, and color coordinate coating amount dependency ofthe rear surface protective sheet according to the present embodiment,an adhesive was produced with the following method and an adhesivenessmeasurement sample using the adhesive was produced.

[Production of Infrared-Light-Transmitting Dark Color Ink (Ink 3)]

[Main Agent]

Aliphatic polycarbonate diol (50 parts by mass) having a number averagemolecular weight of 1000, 1,6-hexanediol (70 parts by mass),1,8-octanediol (30 parts by mass), isophorone diisocyanate (IPDI) (176.6parts by mass), trimethylolpropane (TMP) adduct-modified product (10parts by mass) of isophorone diisocyanate (IPDI), and ethyl acetate(333.6 parts by mass) were filled into a round-bottomed flask equippedwith a stirrer, a thermometer, and a nitrogen gas introducing tube, andthe resultant mixture was heated to reflux under the introduction ofnitrogen gas until isocyanate absorption at 2270 cm⁻¹ disappeared in theinfrared absorption spectrum, thereby preparing a main agent resin ofExample 1 having a glycol modification amount of 10% and a IPDImodification amount of 2%. Incidentally, in this Example, the glycolmodification amount indicates the mass (mass ratio %) of an alkylenediol compound (in this Example, a mixture of 1,6-hexanediol and1,8-octanediol) with respect to the total component mass of the mainagent resin component, and the IPDI modification amount indicates theMass (mass ratio %) of a modified isocyanate compound (in this Example,a trimethylolpropane (TMP) adduct-modified product of isophoronediisocyanate (IPDI)) with respect to the total component mass of themain agent resin component.

The total added amount of 1,6-hexanediol and 1,8-octanediol and theadded amount of the trimethylolpropane (TMP) adduct-modified product ofisophorone diisocyanate (IPDI) were appropriately adjusted so that theglycol modification amount became 10% and the IPDI modification amountbecame 3%.

[Curing Agent]

A curing agent consisting of a nurate product (40 parts by mass) ofhexamethylene diisocyanate (HDI) and a trimethylolpropane (TMP)adduct-modified product (60 parts by mass) of isophorone diisocyanate(IPDI) was prepared. Each blending was carried out so that each NCO/OHratio that is a ratio of the NCO value of the polyisocyanate compound tothe OH value of the cross-linking main agent resin is as presented inTable 5. Pigment: brown pigment (benzimidazolone pigment (Pigment Brown25, particle diameter: 0.08 μm)), phthalocyanine pigment (amorphousphthalocyanine blue pigment (Pigment Blue 15, particle diameter: 0.15 to0.20 μm))

Solvent: ethyl acetate

The main agent, the curing agent, the brown pigment (benzimidazolonepigment), and the phthalocyanine pigment (the content ratio of the brownpigment and the phthalocyanine pigment is 52.5:47.5, the content of thepigment component is 40 parts by mass with respect to 100 parts by massof the main agent resin component) were dissolved in the solvent toobtain Ink 3.

Production of Transparent Adhesive]

[Main Agent]

[Ethylene glycol (32.3 parts by mass), 2,2-dimethyl-1,3-propanediol(270.8 parts by mass), 1,6-hexanediol (122.9 parts by mass), adipic acid(228.1 parts by mass), and isophthalic acid (664 parts by mass) wereadded to a flask equipped with a stirrer and a nitrogen introducing tubein a nitrogen atmosphere, the resultant mixture was subjected tonitrogen bubbling at 180° C. to 220° C. and reacted until an acid valuereached 2 mgKOH/g, and then ethyl acetate (860 parts by mass) was addedthereto, thereby obtaining a 50% polyester diol H solution. The OH valueof the obtained resin was 32 mgKOH/g and the number average molecularweight thereof was about 3500.

100 parts by mass of aliphatic polycarbonate diol having a numberaverage molecular weight of 1000 (product name “DURANOL T5651”manufactured by Asahi Kasei Chemicals Corporation, hereinafter,abbreviated as “PDC 1000”), and polyester diol H (50 parts by mass),1,6-hexanediol (2 parts by mass), isophorone diisocyanate (23.8 part, bymass), ethyl acetate (175.8 parts by mass) which are described abovewere added to a flask equipped with a stirrer in a nitrogen atmosphere,and the resultant mixture was heated to reflux until isocyanateabsorption at 2270 cm⁻¹ disappeared in the infrared absorption spectrum,thereby obtaining a 50% polyurethane diol solution. The OH value of theobtained resin was 14 mgKOH/g and the number average molecular weightthereof was about 8000.

A main agent was prepared by mixing 100 parts by mass of thepolyurethane diol and 15 parts by mass of the aliphatic polycarbonatediol (B) (PDC 1000). Incidentally, the same curing agent as that in Ink3 was used. Solvent: ethyl acetate the main agent (solid contentproportion: 50% by mass), the curing agent (solid content proportion:10% by mass), and 16.7% by mass of the dioxazine compound (the contentof the pigment component is 20 parts by mass with respect to 100 partsby mass of the main agent resin component)

The main agent of the transparent adhesive, the curing agent of thetransparent adhesive, and the solvent were prepared at a mass ratio of18:3.4:5.4.

(Blocking Resistance Test)

A test related to blocking resistance was performed on the samples ofExamples 12 to 15 and Comparative Examples 8 to 10 with the followingmethod, and the blocking resistance was evaluated on the basis of themeasurement results. All test pieces have a width of 15 mm.

An infrared-light-transmitting dark color ink solution was applied ontothe surface of a white PET (White PET manufactured by TORAY INDUSTRIES,INC., 188 μm) film with a bar coater, and the applied ink solution wasdried at 120° C. for 2 minutes to form a dark color ink layer on thebase material surface. Then, white PET (White PET manufactured by TORAYINDUSTRIES, INC., 188 μm) was laminated on the surface of the dark colorink layer immediately after drying to be brought into contact with eachother, and the obtained product after curing at 50° C. for 3 days inthis state was used as a blocking resistance evaluation sample. Ablocking resistance test was performed according to a method ofevaluating the blocking state by peeling off a portion in whichrespective blocking resistance evaluation samples are laminated, and theevaluation was performed on the basis of the following criteria. Theevaluation results are presented in Table 5. Incidentally, the NCO/OHratio in Table 5 is a ratio of the NCO value of the curing agent to theOH value of the main agent resin.

[Evaluation Criteria]

-   A: The dark color ink layer is not transferred, and sheets are    naturally peeled off.-   B: The dark color ink layer is not transferred, and there is slight    sticky feeling at the time of peeling off sheets.-   C: The dark color ink layer is transferred, and/or there is sticky    feeling at the time of peeling off sheets.    (Adhesion Test)

A test related to blocking resistance was performed on the samples ofExamples 12 to 15 and Comparative Examples 8 to 10 with the followingmethod, and the Adhesion was evaluated on the basis of the measurementresults. All test pieces have a width of 15 mm.

An adhesion test according to ASTM D3359 and JIS 5400 was performed andthe adhesion was evaluated on the basis of the following criteria. Theresults are presented as “Adhesion” in the following Table 5.

[Evaluation Criteria]

-   A: 0% of coating peeling-   B: more than 0% and 15% or less of coating peeling-   C: more than 15% of coating peeling

TABLE 5 Blocking NCO/OH ratio Coating amount resistance AdhesionComparative 1.0 4 g/m² A A Example 12 Comparative 3.0 4 g/m² C A Example8 Comparative 6.0 4 g/m² C A Example 9 Comparative 0.5 4 g/m² A CExample 10 Example 13 2.0 3 g/m² A A Example 14 2.0 5 g/m² A A Example15 2.0 7 g/m² B A

From Table 5, the sample of the present embodiment in which the NCO/OHratio of the infrared-light-transmitting dark color ink is set to 1.0 to2.0 has high blocking resistance and adhesion. For this reason, sincethe infrared-light-transmitting dark color ink used in the presentinvention has favorable blocking resistance and adhesion, it is foundthat the infrared-light-transmitting dark color ink is preferable inproduction of the rear surface protective sheet of a solar cell moduleof the present invention.

(Color Coordinate-Coating Amount Dependency Test)

<Sample Production>

Examples 13 to 15

The infrared-light-transmitting dark color ink solution was applied onthe surface of a white PET (White PET manufactured by TORAY INDUSTRIES,INC., thickness: 188 μm) film with a bar coater (the coating amount isdescribed in Table 6), and the applied ink solution was dried at 120° C.for 2 minutes to form a dark color ink layer on the base materialsurface. Then, the transparent adhesive was gravure coated on thesurface of the dark color ink layer immediately after drying (thecoating amount is 5.0 g/m²), the adhesive layer having a thickness of5.0 μm (dry state) was laminated thereon, a polyethylene resin(thickness: 60 μm) was laminated thereon, the obtained product wassubjected to thermal curing by performing an aging treatment at 45° C.to 55° C. for 168 hours to produce a rear surface protective sheet, andthen a pseudo module was newly produced from the rear surface protectivesheet.

The pseudo module was produced by vacuum lamination in such a mannerthat glass as the transparent front substrate, an ethylene-vinyl acetatecopolymer resin (EVA resin) of 450 μm as the sealing material layer, andthe sample according to this Example as the rear surface protectivesheet were laminated in the following order: the transparent frontsubstrate/the front surface sealing material layer/the rear surfacesealing material layer/the rear surface protective sheet.

(Vacuum Lamination Conditions: Temperature of 150° C., Vacuum Time of 5Minutes, Pressing Time of 9 Minutes)

<Evaluation>

Measurement was carried out by irradiating each sample with a lightsource from the transparent resin layer side using a spectrophotometerCM-700d manufactured by KONICA MINOLTA, INC. according to JIS Z8722under the conditions of a D65 light source and a 10′ view angle. Theresults of color coordinates obtained with this test are presented inTable 6.

TABLE 6 Coating Ink amount a* b* L* Example 13 Ink 3  3 g/m² 1.92 −1.415.76 Example 14 Ink 3  5 g/m² 1.77 −1.28 5.88 Example 15 Ink 3  7 g/m²1.57 −1.06 5.53 Comparative Example 3 Ink 2 10 g/m² 5.9 −6.3 —Comparative Example 4 Ink 2 13 g/m² 3.8 −3.2 — Comparative Example 5 Ink2 15 g/m² 3.3 −2.6 8.30 Comparative Example 6 Ink 2 18 g/m² 2.5 −1.2 —Comparative Example 7 Ink 2 20 g/m² 1.8 −0.5 — Carbon black  5 g/m² 0.15−0.48 5.70

From Table 6 and FIGS. 5 and 7, a* and b* in the samples of ComparativeExamples largely fluctuate according to a change in coating amount ofthe adhesive (ink); on the other hand, fluctuation of a* and b* in thesamples of Example according to the change in coating amount of theadhesive (ink) is small. From this result, it as found that theinfrared-light-transmitting dark color inks of Examples have smalldependency on the color coordinate with respect to the coating amount ofsolid contents in the adhesive (ink). L* of the samples of Examples issmaller than that of the sample of Comparative Example 5 in which thecoating amount of the adhesive (ink) is larger than those in Examples,and is equal to L* of carbon black. From this test result, it is foundthat even when the infrared-light-transmitting dark color layer, whichis formed by the infrared-light-transmitting dark color ink thatcontains the brown pigment and the pigment component containing aphthalocyanine pigment component, has a small thickness, theinfrared-light-transmitting dark color layer has sufficient designattractiveness. For this reason, for example, when theinfrared-light-transmitting dark color layers are intended to belaminated for partially coloring the transparent adhesion layer and/orthe reflective layer from the viewpoint of design attractiveness, theuse amount of the transparent adhesive can be decreased. Therefore, itis found that the infrared-light-reflecting sheet of the presentinvention is an excellent infrared-light-reflecting sheet which canreduce costs and improve productivity.

(Adhesion Test)

<Sample Production>

An infrared-light-transmitting dark color ink solution was applied onthe surface of a white PET (White PET manufactured by TORAY INDUSTRIES,INC., 188 μm) film with a bar coater (the coating amount is 4 g/m²), andthe applied ink solution was dried at 120° C. for 2 minutes to form aninfrared-light-transmitting dark color layer on the base materialsurface. Then, the transparent adhesive was gravure coated on thesurface of the infrared-light-transmitting dark color layer (the coatingamount is 5.0 g/m²), a transparent adhesive layer having a thickness of5.0 μm (dry state) was laminated thereon, a polyethylene resin (60 μm)was laminated thereon, and the obtained product was subjected to drylamination and then subjected to thermal curing by performing an agingtreatment at 45° C. to 55° C. for 168 hours, thereby producing aninfrared-light-reflecting sheet sample.

The conditions in a pressure cooker tester (HASTIEST manufactured byHIRAYAMA MANUFACTURING CORPORATION) were set to 120° C., 85% RH, and 1.6atm, the above respective samples were input thereto for a certain time(in Table 7, “before input” is described as 0 h, and “after input for 24hours” is described as 24 h and the like). Thereafter, the peeling testwas performed three times. An average value of each measurement resultbefore input and after input for a certain time is presented in Table 7.Incidentally, the NCO/OH ratio in Table 7 is a ratio of the NCO value ofthe curing agent to the OH value of the main agent resin.

TABLE 7 0 h 24 h 48 h 72 h NCO/OH ratio [N/15 mm] Comparative 0.5 9.57.8 5.2 3.6 Example 10 Example 12 1.0 10.4 11.6 12.5 9.1

From Table 7, it is found that the sample of Example 12 in which theNCO/OH ratio is 1.0 to 2.0 is a sample having higher adhesiveness andhigher adhesiveness durability than Comparative Example 10.

EXPLANATION OF REFERENCE NUMERALS

-   1 SOLAR CELL MODULE-   2 TRANSPARENT FRONT SUBSTRATE-   3 FRONT SURFACE SEALING MATERIAL LAYER-   4 SOLAR CELL ELEMENT-   5 REAR SURFACE SEALING MATERIAL LAYER-   6 INFRARED-LIGHT-REFLECTING SHEET (REAR SURFACE PROTECTIVE SHEET)-   7 INCIDENT LIGHT-   60 INFRARED-LIGHT-TRANSMITTING DARK COLOR LAYER-   61 REFLECTIVE LAYER-   62 TRANSPARENT ADHESION LAYER-   63 TRANSPARENT ADHESIVE LAYER

The invention claimed is:
 1. An infrared-light-reflecting sheetcomprising an infrared-light-transmitting dark color layer and areflective layer, wherein the infrared-light-transmitting dark colorlayer contains a first pigment and a second pigment, the first pigmentis at least one or more pigments selected from the group consisting of abenzimidazolone pigment,4-[(2,5-dichlorophenyl)azo]-3-hydroxy-N-(2,5-dimethoxyphenyl)-2-naphthalenecarboxamide,1-[(4-nitrophenyl)azo]-2-naphthalenol,bis[3-hydroxy-4-(phenylazo)-2-naphthalenecarboxylic acid]copper salt, C.I. Pigment Brown 7,N,N′-bis(2,4-dinitrophenyl)-3,3′-dimethoxy-1,1′-biphenyl-4,4′-diamine,3,4,9,10-perylenetetracarboxylic diimide,Δ2,2′(1H,1′H)-binaphtho[2,1-b]thiophen-1,1′-dione, andN,N′-(10,15,16,17-tetrahydro-5,10,15,17-tetraoxo)-5H-dinaphtho[2,3-a:2′,3′-i]carbazole-4,9-diyl)bis(benzamide),and the second pigment contains a phthalocyanine pigment, wherein alight reflection rate of the infrared-light-reflecting sheet is lessthan 15% when light having a wavelength of 700 nm to 750 nm is incidentto the infrared-light-reflecting sheet.
 2. The infrared-light-reflectingsheet according to claim 1, further comprising a transparenteasy-adhesive layer laminated on the surface on the lamination side ofthe infrared-light-transmitting dark color layer of theinfrared-light-reflecting sheet.
 3. The infrared-light-reflecting sheetaccording to claim 1, wherein the infrared-light-transmitting dark colorlayer contains a main agent resin having a hydroxyl group, and a pigmentcomponent, a content of the pigment component is 20 parts by mass to 40parts by mass with respect to 100 parts by mass of a resin component,the pigment component contains a first pigment and a second pigment. 4.The infrared-light-reflecting sheet according to claim 3, wherein acoating amount of an infrared-light-transmitting dark color ink formingthe infrared-light-transmitting dark color layer in terms of solidcontent is 5 g/m² to 15 g/m².
 5. The infrared-light-reflecting sheetaccording to claim 1, wherein a color difference ΔE*ab between a colortone of the infrared-light-transmitting dark color layer and a colortone of carbon black as measured under conditions of a D65 light sourceand a 10° view angle according to JIS-Z 8722 is 10 or less.
 6. Theinfrared-light-reflecting sheet according to claim 1, wherein aninfrared-light-transmitting coat layer is laminated on a surfaceopposite to the lamination surface of the infrared-light-transmittingdark color layer of the reflective layer, and theinfrared-light-transmitting coat layer is a layer containing an organicdark color pigment and transmitting near infrared light having awavelength of 750 nm to 1500 nm.
 7. A solar cell module comprising theinfrared-light-reflecting sheet according to claim 1 and a solar cellelement, wherein the infrared-light-reflecting sheet is disposed on anon-photoreception surface side of the solar cell element.
 8. Theinfrared-light-reflecting sheet according to claim 3, wherein a colordifference ΔE*ab between a color tone of the infrared-light-transmittingdark color layer and a color tone of carbon black as measured underconditions of a D65 light source and a 10° view angle according to JIS-Z8722 is 10 or less.
 9. The infrared-light-reflecting sheet according toclaim 3, wherein an infrared-light-transmitting coat layer is laminatedon a surface opposite to the lamination surface of theinfrared-light-transmitting dark color layer of the reflective layer,and the infrared-light-transmitting coat layer is a layer containing anorganic dark color pigment and transmitting near infrared light having awavelength of 750 nm to 1500 nm.
 10. An infrared-light-reflecting sheetobtained by laminating a plurality of layers, the plurality of layersincluding at least: a transparent adhesion layer transmitting lightbeams; and a reflective layer reflecting light, wherein two layers amonglayers laminated between the transparent adhesion layer and thereflective layer are an infrared-light-transmitting dark color layer anda transparent adhesive layer, the infrared-light-transmitting dark colorlayer contains a first pigment and a second pigment, the first pigmentis at least one or more pigments selected from the group consisting of abenzimidazolone pigment,4-[(2,5-dichlorophenyl)azo]-3-hydroxy-N-(2,5-dimethoxyphenyl)-2-naphthalenecarboxamide,1-[(4-nitrophenyl)azo]-2-naphthalenol,bis[3-hydroxy-4-(phenylazo)-2-naphthalenecarboxylic acid]copper salt, C.I. Pigment Brown 7,N,N′-bis(2,4-dinitrophenyl)-3,3′-dimethoxy-1,1′-biphenyl-4,4′-diamine,3,4,9,10-perylenetetracarboxylic diimide,Δ2,2′(1H,1′H)-binaphtho[2,1-b]thiophen-1,1′-dione, andN,N′-(10,15,16,17-tetrahydro-5,10,15,17-tetraoxo)-5H-dinaphtho[2,3-a:2′,3′-i]carbazole-4,9-diyl)bis(benzamide),and the second pigment contains a phthalocyanine pigment, wherein alight reflection rate of the infrared-light-reflecting sheet is lessthan 15% when light having a wavelength of 700 nm to 750 nm is incidentto the infrared-light-reflecting sheet.
 11. Theinfrared-light-reflecting sheet according to claim 10, wherein a coatingamount of an infrared-light-transmitting dark color ink forming theinfrared-light-transmitting dark color layer in terms of solid contentis 3 g/m² to 7 g/m².
 12. The infrared-light-reflecting sheet accordingto claim 10, wherein the infrared-light-transmitting dark color layercontains a curing agent having an isocyanate group, and wherein thecuring agent is a diisocyanate compound.
 13. Theinfrared-light-reflecting sheet according claim 10, wherein theinfrared-light-transmitting dark color layer is laminated only on a partof the surface of the transparent adhesion layer and/or the reflectivelayer.
 14. The infrared-light-reflecting sheet according claim 11,wherein the infrared-light-transmitting dark color layer is laminatedonly on a part of the surface of the transparent adhesion layer and/orthe reflective layer.
 15. The infrared-light-reflecting sheet accordingto claim 10, wherein an infrared-light-transmitting coat layer islaminated on a surface opposite to the lamination surface of theinfrared-light-transmitting dark color layer of the reflective layer,and the infrared-light-transmitting coat layer is a layer containing anorganic dark color pigment and transmitting near infrared light having awavelength of 750 nm to 1500 nm.
 16. A solar cell module comprising theinfrared-light-reflecting sheet according to claim 10 and a solar cellelement, wherein the infrared-light-reflecting sheet is disposed on anon-photoreception surface side of the solar cell element.
 17. Theinfrared-light-reflecting sheet according to claim 10, wherein theinfrared-light-transmitting dark color layer contains a main agent resinhaving a hydroxyl group and a pigment component, the content of thepigment component is 20 parts by mass to 50 parts by mass with respectto 100 parts by mass of the main agent resin, the pigment componentcontains a first pigment and a second pigment, wherein an NCO/OH ratiothat is a ratio of an NCO value of the curing agent to an OH value ofthe main agent resin is 1.0 to 2.0.